No worries, they can be a pain if youve never used a Lian Li before.
They have these little nipples on each side, on the inside of the drve cage, you need to pick a side, I usually take the right on, pull inwards on the tab while pushing foreward and the cover will move out. Now do the same on the left.
Go round to the front, and then pull it out a bit more, then bend in the tabs to get the nipples away from the case front.
Do this twice, and you should be able to feed the drive in.
The door is open of all of this, if you are still having trouble let me know as I can make you a instructional video.