one is the squares, and one is the sheet. I always discourage the sheet because if something drops and you tear the vinyl you cannot properly patch that area, but with squares, you just remove that square and walla, insert a new one. Always but an extra box for just this reason.
Now, in a small nutshell here is the approach. remove all the old flooring to the slab, or if the old is in good shape, you can go over the old with no problem. I only go over one layer only. Then if the old has some bad spots, just remove that square and lay down a dummy square to fill in and make all even.
sweep, dry vac, and remove all debris. The smallest particle will cause a high spot on your new flooring and will show and wear the quickest. Constantly be sweeping and cleaning the floor as you go.
Next, if you have any cracks, dents, or divots, use a good floor levelor to smoothe out the sub floor, so all is nice and even.
Actually, this should be number one, but, buy a good quality and thick tile. If you scrimp on quality, you will be doing this again in a short time. Get a thick tile and get a tile that has super holding glue on the back. I always tell my future customers to pull back the back skin and see how sticky the glue is. it must be strong.
Now, I like a very symetrical flooring. meaning that any partial tile on the left is the same on the right. This is done by laying out the tile the width and lenght of the room. Now you can shift to one side or the other to make it the same on each side. I hate to see flooring with a hole piece on the right and as they worked to the left, the space is only 1/3 the tile. Split the difference and make it even.
I do not recommend using any mastic or glue on the clean slab especially if you have a good quality tile with glue backing. The reason, in our area, in the summer the glue will leach up through the cracks and become a total nightmare.
Now lay down the tile work in front of you going back to the workout area.
Look on the back of the vinyl tile and you will see an arrow, that means that even though the tile are the same, they must be laid down all the same way, the arrow usually designates the direction in which you are laying.
After done, lay down the moulding and during the next 24 hours lightly walk on the project and making sure that all the corners stay down. if you have a corner that seems to stay up, use bricks or books.
Should be fine to walk on with reg traffic in 24 to 36 hours. Settles down faster if the room is warm.