Does anyone know how the drive belt on an old Murray 11-36 Mower should be put on.

Question

At the moment the gears work but the brake and clutch are reversed. You must keep your foot on the clutch to run.When you take your foot off the clutch the mower stops.

Answer 1

Sounds like you have the belt routed wrong.  Watch the brake/clutch pulley as someone steps on the pedal.  It should be obvious how it goes.  Look under the foot rest, there may be a belt routing decal under there.  

Answer 2

Your drive belt is on the wrong side of your belt tensioner.