Is this Wilbur? If he was a camp horse he may have spent a lot of time being led and never been taught or just forgot any cues. You may want to enlist some help and have someone lead him while you give verbal/hand/leg cues. Hopefully he will put it all together. If not you may have to go back to basics on groundwork. I start with a verbal "kiss" then hands forward then leg pressure for forward movement. I always "tsk" or "kiss" to walk out even on a lead rope so hopefully they will transfer that sound to the same thing when under saddle. I know he is new to you so hope you will get lots of suggestions from other folks to help you out. :)
"Until one has loved an animal, part of one's soul remains unawakened..."
- Anatole France