There are a couple of ways to make a black outline around a print. The easy way is to use a larger size glass negative holder. Unfortunately, that usually leaves evidence of the film edges.
The second way is much more complicated. First you cut a piece of opaque cardboard to the size of the desired image (e.g, 7-1/2 by 9-1/2 for an 8X10 print with 1/4 inch boarders). Next you set up the enlarger to make the print, using a boarderless easel. If you do not have a boarderless easel, mark the paper position on the easel so that you can place the paper in the right spot for a boarderless print, attaching it with removable 2-sided tape. Put the paper in place, and make the exposure. Place the opaque cardboard over the image area, remove the negative, and make another exposure long enough to fog the boarders. Process as usual. This may take a couple of tries to get the alignment right.