Adding Thumbnails to my gallery

Hi, once again it’s the dummy who try to realize the tutorial and who need help.

Actually, I try to adapt the tutorial “adding thumbnails” to my gallery. But Not as the tutorial, I try to have them not on 1 line but on a grid. I adapt the boundarys (left and right) by (top and bottom) change in the code their name.

Basically it’s working but all my thumbnails are in the same spot on a top of each other)

Could you help me to undersand how to place my thumbnails (3 in a raw and … in a column)

I placed my thumbnails area on the left My images area is on the middle and my text zone is on the right.

Help me, please.

Thanks in advance.