Privilege Escalation
Once you have achieved a shell onto a Linux box, the next thing you want to do is elevate yourself to root privilege. There are a lot of ways to achieve privilege escalation, so most of the time beginners will use a tool to help them find attack vectors.
My personal favourite is LinPeas. If you can get the bash script onto the target machine and execute it, it will provide you with a huge output highlighting many potential entry points. It takes some time to comb through this output, but often this will get you to an escalation pathway.