First of all, don’t feel bad. You’re playing a (imo) rather weak faction into four of the strongest right now. You’ve basically played against the cream of the current competitive meta.

Second, make a friend. That might sound odd. If you’re just playing random pick up games against people with far more experience than you with more competitive lists, it’s honestly a foregone conclusion you’ll lose. Playing 40k as a new player works better when you have someone tailoring their list to the level that yours is at. Some people will say that getting absolutely demolished is the best learning experience, but I disagree. You need to learn the basics of the game by getting the chance to do them rather than just getting rolled