Cavalry for beginners
Small units, cheap, things you’re not afraid to use. Scouting with an 1000 coin, 50 man unit is not the best use of that unit. Most cheap scout cav double as arty and skirm snipers. Lancers do not have the sight range that regular light cav have so they do not make ideal scouts, although Cossacks are acceptable because they are usually cheap and can hold their own in a light cav engagement. C8/C9 is ideal but C7 is fine. As a reminder, C8 are flat out faster than C9 but C9 are more maneuverable.
Lancers and irregulars
Lancers receive a ×2.5 modifier to their listed charge bonus, and also -3 to their stated melee defense. I believe these are both hard coded from CA. So if the Schwarzenburg Ulanen from 1809 Austria charge you, their 5 charge + 12 melee means they actually hit (assuming a good, solid charge) at 24.5 initially. Absolutely painful for all light cav, and dragoons and heavies usually need to watch out. Lancers are well suited for flank charges, but they will usually trade upwards against light cav due to overall low defense light cav has.
Their big downside, as mentioned above, is they don’t see as far as regular light cav, so the enemy will likely see your lancers before you see them. Lancers will also suffer in long term engagements, so charge, get the damage, stay a few seconds to see if the enemy breaks, then get out and repeat. If ever you get the chance to flank/rear charge heavies or dragoons, do it. The results can be devastating. You can break Les Dieux with a trio of Cossacks and well timed charges from all sides. Irregular cav is a blanket term for the bow and gun armed cav found mostly in eastern nations. Both are really fun to use against heavy cav that lacks light cav support, and both are great if left on the flank/rear of a cav fight to just shoot into it. Usually they are cheap and make good scouts, but have that extra bit of harassment ability from range.
Light cavalry superiority
Medium to high tier light cav, usually with 35-50 men, with decent morale and 13+ melee (and ideally for good quality 16+ melee). The larger the unit size, the more value you get out of them as tanks (Austrian Chevaulegeres, Russian Gusari) while other light cav skirt around the flanks and side- or rear-charge. Ideally, no matter what role, you should usually run your light cav around in pairs so they can support each other better, as well as have a wider frontage for screening and scouting. Bonus points for pairing decent light cav with lancers.
Light cav superiority is meant to aggressively scout the enemy while also screening your own forces. You’re bullying the other player’s lights. For light cav superiority, your units should be able to win a local light cav engagement, but also be able to run away if enemy dragoons or heavies make an appearance. We'll talk about full cav superiority later.
Full cavalry superiority
Just like light cav superiority, full cav superiority is about pushing back and bullying your opponents cav but on a grander scale than just light skirmishes. In this case you want to force a full cav engagement that you know you will win, removing most or all opposing cav local to you, and allowing you to press the enemy infantry line better. If you lose most or all of your cav in an engagement, even one that kills most or all of the enemy cav, you’ve failed in your objective. The idea is to have enough cav going forth into the late game with no opposition. Heavies and dragoons are good tools, and you need the lights to force the engagements, as the enemy may try to pull back. Engaging enemy cav near their inf or arty is not advised, as bullets and canister will quite possibly turn fights you would have won against you. Likewise engaging near your own troops, if possible, is great. Skirmishers and quick (L5+) squarables are wonderful support tools for this kind of grand cav engagement.
Your light cav should force the engagement by either threatening to rear charge enemy dragoons or heavies as they run away, or overwhelming your opponentments micro and catching a stray unit or two. After that, if the enemy commits, your dragoons will be your initial tanks, taking advantageous charges (from lights or weaker dragoons) or tanking enemy heavies while your own heavies catch up to relieve them. Having a cav combat gen or your own staff gen nearby will help keep your men from routing. If possible, pursue all fleeing units below half strength, as an enemy dragoon returning because you forgot about could have terrible ramifications in the future.
Ideally you will have one unit of cav per unit of guns to act as protection. Good units for this are medium tier light cav or low tier dragoons. Things you won’t miss from the front, but in a pinch can protect your artillery from rushing enemy light cav (that has probably also been damaged on the way in). Guarding with heavy cav is doable but never ideal, as, if you are close enough to effectively protect the guns with the slower speed of the heavies, you are quite possibly taking counter battery shots from the opposing side. Also, units with higher mass will cause friendly fire on the charge, so charging a heavy through your artillery will likely kill them if the enemy cav has gotten close enough.
While light cav and lancers can support infantry, both offensively and defensively, this is the true realm of dragoons and heavies of all qualities. After all, a low tier 80+ man dragoon charging your line is still going to hurt and probably break it. Defensively, poor quality dragoons and heavies are excellent as units to counter charge enemies that are threatening your line, as they don’t have to risk themselves until the enemy is already committed to an attack. Offensively, medium (or higher) quality dragoons and heavies are phenominal, as their (usually) large unit size and morale means they can take more damage on the way in, and the higher attack and charge value can devastate whatever they hit.
However, you should obviously avoid clumping all your units up and having them charge over each other. Other than the friendly fire from charging into your own back, you're also just an easy target, and clumping provides no real benefit. Ideally, you have cav superiority in this scenario, so that no enemy cav can counter charge you, further disrupting your morale and unit cohesion. Even if the cav countering you is bad, they will still hold you long enough for the infantry to reform. And bullets don’t care about your melee defense.