Easiest way to do it is actually in the editing of the beatmap.
You go to file then upload beatmap.
After you fill in your options you just upload it and it goes straight to the website.
Then send the link of the page to a friend
I think the easiest way is to actually just export your beatmap in the options in the top left corner, and then send it to them over Google Drive/Discord or any other site for storing files.