This is Fun level 1, "Start with nothing, end with nothing". You have 100 lemmings and have to save all of them. You have 8 minutes, which is plenty of time.
Your lemmings will start with no items. Your lead lemming will pick up a Builder ability.
Your lemmings can't climb up the little ledge in front of them. Make a lemming into a Builder so they can get up.
Your lemmings will them pick up a Miner ability.
Change a lemming into a Miner, right in front of the right wall to dig through it.
Now the lemmings will pick up a Basher ability.
Change a lemming into a Basher, right in front of the column that blocks your path.
Once through the column, there will be another Miner ability they will pick up.
Make a lemming into a Miner so that you dig a diagonal tunnel all the way to the bottom. Careful because the light-colored crates with an X on them are impenetrable.
Your lemmings will climb up the grated material on the right, then they'll grab a Digger ability.
Scroll back over to the entrance of this level. Use the digger to dig down. Just be careful not to dig right under where the lemmings are entering the level, otherwise they'll fall to their death.
Now all your lemmings will exit. Increase the rate lemmings enter the level by using L1/R1 to select the + on the menu below. Press X on this and increase the value to 99. The lemmings will start pouring out the entrance.
Hold down the O button to speed up the rest of the level and watch all the lemming exit safely.
Success! Press X to continue to the second Fun level.