You can access the LIMBO using the "Essence of LIMBO" which you can find in two places
if you want a really hard survival challenge you can turn the bonus chest on in "More World Options" when generating a world and the essence spawns in the bonsu chest
Or you can go to the end and find a Essence in one of the End city chests
Once you found an essence put it in your hotbar and select it when you want to teleport
You won't be able to leave the limbo until you completed the progression of the dimension (suggestions are welcome)
Collect all the wither flowers and "Limbo Scrap" they will come in handy
Craft a fishing rod as soon as possible using strings from dispenser loot and sticks from leaves
You can find dirt on steep cliffs ususally near water
After getting dirt you want to break some leaves and get oak sapling
Grow the sapling into a tree to craft a pick to mine blackstone
Craft an oven from the blackstone
This is all I'll tell you, the rest is up to you to explore