I really wanted to take a user input and force it to be a floating point number not a string (for math equations), but I could only find a way to take user input and make it an integer int(<STDIN>), but what if they enter a number with a decimal?

You've gotten some good answers already, here is a short one :-) Perl automagically converts between strings and numbers, including decimal numbers. If a variable contains a string that looks like a number, and you use it in an operation that normally involves numbers, Perl will do the conversion for you.

my $input = <STDIN>;
chomp($input);         # remove newline
my $output = $input + 1.23;
print "output: $output\n";
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Now for example, if you enter "3.45", the output is "output: 4.68". Perl has automatically converted $input from "3.45" to 3.45 for the addition, and converted $output from 4.68 to "4.68" for the "output: $output\n"!

When I look things up, it feels like I'm diving into the deep end and I can't see the shore.

I know the feeling as well - looking things up in the official Perl documentation sometimes has that effect, because you get all the details at once. Fortunately, there are tutorials, for example on this site, as part of the Perl documentation (for example perlintro is a good start), and of course there are books such as Learning Perl that give a slow introduction without overwhelming with all the details.