I'm guessing here... You have downloaded fastqc, trimgalore etc. Now you want to put them in one of the directories listed in the PATH variable so that when you login you can execute e.g. fastqc without specifying the full path to fastqc. Usually, you do this by moving the programs of interest to ~/bin or ~/.local/bin. These directories may already exist and be in $PATH, if not create them and edit ~/.bashrc to add them. But do echo $PATH to see first what you already have.
Having said that, I suggest installing conda and bioconda and let conda manage program installations for you.
as dariober mentions below: your .bashrc (or .zshrc, .cshrc ... depending on what shell you use) file is the way to go to get this done.
I will not comment on the feasibility/usefulness of what you try to achieve ;)