Just keep playing the game and expose yourself to the game's elements. I started on Minecraft Alpha a long time ago and kept playing it and visiting the wiki until I've learned a good amount of the game. You can also join a server and play with others—I'm sure there are plenty out there who will be wiling to help out a newbie learn the game.
And yeah, you probably should get a better PC to enjoy the most out of Minecraft. I have an Intel i7 4-core 4.00 GHz, 16 GB ram, and GeForce GTX 1060. The game runs really well for me. Though, my computer is probably overkill, you don't really need that high of stats. Just giving an example.