We know what size means. Underline, of course underlines the text, and baseline will drop characters below the baseline. For example, the first letter of a word can be lower than the rest of the word by selecting the first letter, and setting a baseline value. Kerning effects the width of the text by effecting the actual characters. Positive kerning would have made the word wider.
Tracking also effects the width of the text by effecting the space between the characters.
Leading effects the space between lines of text.