In Vim, if you want to find a word in a text, you run /something, then hit enter and move between the results with n / p (see :help search-commands).

By default it's case-sensitive, so if you have a text like this:

This is something. Something is good. sOmEtHing!

It will only find the first something (with lowercase s).

If you'd like to capture all occurrences no matter which case is used (case-insensitive search), you can append \c to your search pattern, like this:

/something\c

If you want this behavior by default, you can turn on the option:

set ignorecase

There's also a so-called "smartcase" (:help smartcase) which works as case-insensitive if you only use lowercase letters; otherwise, it will search in case-sensitive mode.

set smartcase