There is a plug and minus sign. Use the plus to add a user, minus to remove one.
Steps: Option i to get info, look at the very bottom of the window that opens, look for sharing and permissions. Point the arrow down. If you see no accounts, use the plus sign to make one, and then change the permissions to read write.
The other thing we didn't as was this: if the files came from a PC, each file would have to be unlocked.
Same thing: get info, and then uncheck the "locked" checkbox.
When you get home try these, mainly because doing this stuff from memory is impossible, even for someone who has bee doing tech for almost 3 decades ;-)