Most kerning happens automatically using the kerning tables built into the various fonts (assuming you are using a font with an embedded kerning table). There is a Kerning value in the "Scene Fonts" tab to adjust the overall amount of kerning.
If you want to perform manual kerning, it must be done on an object that is not published to the sequencer. From within layout you can select the textobject and postion the cursor where you want to kern, then use the hotkeys CTRL + PLUS (on the numpad) and CTRL + MINUS (on the numpad) to adjust the kerning between individual letters. Again, note the text object must not be published, or your kerning will be overwritten if the scene is put online from the sequencer.
#XPression