Checking out should be done within UEFN, right click the files you want to check out and there should be a source control menu with check out.
UEFN will also handle checking out files if you forget to (It will want to check out on save)
P4V at this point is just used for getting latest changes and also committing .verse changes.
When getting latest always have the project closed.
To commit .verse files right click them in p4v and click “Add” to add to change list, then “Submit” to well, submit it.