I decided to try my hand at kerning, but the menus aren't behaving like what Design w/FontForge says it should. (Look to my sample for context). I thought that I should make the 'X' and 'T' a kern pair (look for "EXTRA" near the bottom), so I selected "Kern Pair Closeup..." then gave the 'X' and 'T', and reduced the kern offset to -300 so that they are on top of each other. It also asked me to make up this "subtable". I had no idea what I was doing there, so I just gave "XT" and it selected "XT-1". Unfortunately, I don't even know how to get back to those dialogues. When I gave it the old college try (meaning a TTF), it all had no effect--I didn't see any change to the spacing to 'X' and 'T'.
I have even less success w/Kern By Classes. That just gives me a window with only "New Lookup" and "Done" enabled, and "New Lookup" just gives me another dialogue with "XT" and "Create new lookup". If I select "Create new lookup" the dialogue disappears, but otherwise nothing happens.
I’m almost as confused as you are, but I got it to work for me. Here are a few notes that might help.
The place to go to see what lookups you have, see what’s in them and edit them is Menu, Element, Font Info, Lookups, GPS tab.
A lookup table is just a holder for subtables. All the actual kern data is in subtables.
You would probably want all your kerning pairs to be in one lookup table, so you should not name the table for a single kern pair. When you select “New” for a table or subtable you get a default name. The default name is usually as good as any.
You would usually have many kern pairs in a subtable. You could also have more than one subtable in a lookup table. The subtables in each lookup table are looked up in sequence for each pair of characters, and as soon as a subtable is found that includes that pair, referencing that lookup table stops and the next lookup table is looked up.
In that page in “Design with Fontforge” about “Spacing, Metrics and Kerning” scroll down to the subhead “Kerning with Classes” and carefully read everything below it except the sentence fragment “The same interface is also got at via the.” Then you can read the rest of the page.
I guess my problem here was that I did something that FF didn't expect, which caused the weird behaviour. Following those instructions exactly did get me some distance, but now it crashes pretty often. It seems I have to save my work every 30 seconds.