You are not allowed to upload anything you didn't create yourself unless you have permission from the original creators. I doubt you are allowed to upload the freeware fonts you found, but the ones your friends said you can upload are okay.
To upload them, put the font file(s) in a .zip or .rar archive and create a preview image (.jpg, .gif, or .png) showing what's in the file(s). You can look at other people's deviations for examples.
You zip the font files, upload the zip on the dA submission page, then it will ask you for a preview image. Upload the preview image (jpg, gif, or png), make sure you fill out the rest of the submission requirements, then submit.