Those where not jokes...just a little levity.
What the %$^& makes me so funny, huh??? (insert Joe Pescie here)
Yup, you are right about attaching the two side cabinets. You will need some shims or blocks between the cabinets to help hold them together.And use some clamps to help hold them at first.
Or you can screw through the face frames which will hold better.
But you need to pre-drill first.
You also need to find the highest part in the floor area to start, otherwise you will be cutting the bottoms of the cabinets to get them level all the way across the kitchen.
Then shim them to where they need to be and install a toe kick at the bottom to meet the floor and cover the shims.
Also install a cleat(board) to the back wall behind the LS to hold the counter top. Do this when you have the cabinets at the correct hieght.
Home because of rain today, you lucked out.
Good luck Shan.