Might sound stupid, but the number 1 thing to learn in this game is how to survive. Actually dealing damage is secondary and can come later. I'd suggest learning to manually block so that its at least some fun while you learn to survive rather than just holding down right mouse with a shield. Main things to learn imo for survival:
Know when to run and when to fight. Make a mental note of how many team mates you have in the area and how many enemies there are, and refuse to engage in a fight that you think you have little chance of winning. You need to be aware of how many team mates you have alive compared to the enemy though, it might be that you have to take a risk and engage outnumbered sometimes. Generally though with evenish numbers on each team you should always retreat when outnumbered and regroup. If you have more players alive than the enemy then you don't ever have to fight outnumbered and you should regroup rather than fight an even fight and then lose the round. As you get better you can take more risks, but to start just be passive and learn to survive as long as you can while still having some impact on the round. Some rounds have an initial melee phase that you can't really retreat from without losing the round though, theres a bit more to it than I've put here.
Rebind the "view outfit" key or get used to pressing it constantly. Its the ` (left of 1) by default. I have this as the b key and I'm pressing it 90% of the time when I'm not fighting. You need this to be aware of your surroundings and to avoid cavalry.
Teamwork is king in this game. If you help your team to survive you win, but you have to balance it with knowing when you should be retreating. Helping a guy survive in the short team might not help you win the round in the long term if there are too many enemies nearby.
Learn to recognise people on the field and what their strengths and weaknesses are. Check tab to see who is alive and what clan they're in. Even if you think you have the round won, you might press tab and see someone who can actually win the round for the enemy. You might see a key player knocked down and jump in and block for him, or you might be a distraction to help someone who's in a bad situation. Remember the first point though, helping guys out that are outnumbered can just end with you both dying which is no good for anyone. But you might decide its worth you dying if you help a particular player survive
Don't fight 1v1 if you can help it. If you're group fighting then be aware of people making sneak attacks on you, and you should rotate around who you attack. So don't tunnel vision on one guy, take a look to the side and maybe help a team mate while you block the other one. People tunnel vision a lot in this game and think they're 1v1ing when they aren't
Try not to look like an easy target. Stay with team mates, wear medium gear at least with a decent helmet and boots. Even if the armour doesn't help all that much, if you look like a peasent people will try to take you out of the picture first as it will take more effort to kill the other guys. I think this is one of the key reasons new players die early, they just look like an easy target because of something they do or how their gear looks. It might seem unfair, but you get fake peasants that actually can cause a lot of problems, and 1 less distraction is worth like 1 or 2 hits if its an easy kill.
Use a balanced build and gear. You need some speed, some HP and some damage imo. I used to always go 21/18 builds with a 2 hander until I stopped retiring. I would go 21/18 with a polearm now. 7IF,7PS,6Ath, 3 WM I think it is. Lots of viable builds though
Probably a bunch I left out but maybe this can help. This is a game that will suck you in as you get better, try to enjoy learning to play rather than get frustrated. You should only get frustrated if you aren't really learning much as you play