You can use gallery-dl, it's a command line program but it's simple and supports a lot of sites.
i've tried installing it but it gives me a lot of errors i don't even know where to begin
If you have no idea where to begin, asking the good people on reddit: /r/DataHoarder or some other sub would be a good place to start.
If you've narrowed down your issue to a replicable test case, opening a new issue at gallery-dl would get you better support.
The simplest way to set it up i guess is to download the .exe (if you are on windows) from here
Then you have to navigate to that dir in the command line, the easiest way is to type cmd in the address bar where you have gallery.exe like
And then you just type gallery-dl https://www.redgifs,com/users/randomuser