Having Hard time - learn elgg

Hey guys, i have use elgg for like 8 moth but i still cant understand core ideas like how to create theme, plugin.. i mean i know what i have to do like create a folder in mod and create file start.php,mainfest.xml and so n so ...ma problem is i cant extend views and change there style ,create ma own plugin that add features update database so i want if someone give me some idea or resource. i know php + javascript,jquirey,css....