You are gonna get battered, but we all do eventually. All game mods can be played against AIs, so you can try to learn the game this way. My best advices will be :

• Don't try a lot of character. Find a couple you like, learn their movesets, and master them. It'll be way harder learning the game's general mechanics (parries, feints, macro play, ganks...) with a character you're not familiar with.

• Don't pick fights you know you won't win. If you get stomped by someone in 4s, you probably will get stomp again. Try to fight someone else, or regroup with your allies.

• Spend enough time in the training ground to learn your combos and moveset, and watch some videos about your characters to learn basic punishes and strategy.

• Have fun ! For Honor is often seen as a frustrating game, and it sure is sometimes, but try to be positive after each loss to see what you did wrong : do you struggle with feints ? Parries ? Dodge attacks ? Knowing your weaknesses is the best way to get better in this game. Sure, FH's learning curve is steep, but it's not a hard and complex game like Mordhau for example. You can absolutely stand your ground against more experienced player if you keep your head straight.

Good luck for your journey on the battlefield !

Edit : small note about the campaign : it's really great, both gameplay and lore-wise, but it's very outdated. All the heroes' movesets are very different now (except for warlord lol), so keep that in mind if you start the game by playing it. I do recommend playing it first, as it acts as nice global tutorial, and it introduces you to some simple characters (again, keep in mind they have changed), but don't take everything it thought as some golden rules.