I have a problem installing plug-ins

I have a problem when trying to install WordPress plugins. My problem is that when I add php code, directly and i am afraid that I will drop the blog. I’m trying to go from blogger to wordpress, that’s why I found complicated the blog. Hopefully I can advise that it is quite complicated and do not know where I add the code of each plugin. Thanks for the help.

Pd: I am Spanish, forgive me about my language use.