Been looking for font to put into a Youtube video for commercial purposes. I found a few, and all the information says is "Free". I'm not entirely sure what that means. Does it mean we are able to use it without credit? Does it mean we can use it without asking, as long as we give credit? Or does it simply imply that we do not have to pay to download it?

If a font is free, you can use it for personal or commercial use, without paying anything to the creator. You also don't have to ask first before using the font.

If you are using a free font available at dafont, adding a comment, and perhaps an image or other link to the font in use would be appreciated by any designer.

You're not allowed to 'knock off' a free font, (ie: rename it, claiming that you are the designer), which you could do for something that's public domain.

No, "Free" don't mean "public domain". It mean that you don't have to pay to use it.

To use a free font for a commercial project, the best is to contact the creator and to clear that with him.