Did you Subscribe to them first? Then when you pick a world to load, don't load first go to Edit Settings then click on mods button. Then your mods should load on left half, use arrow in middle and move the mods from left to right as you select them. Hit OK then OK again, then load your map.

Thanks for replying, I figured it out, I had to pick the mods when I loaded the world, thats for your help though!