"does it need to be attached to the wall or floor"
A DIYer comment here. If the bath is a plastic/acrylic type, it is likely to come with some mounting brackets and a pair of support frames. In my opinion, these are never very sturdy and, in time, the bath will move and break any seal or tiling which it might be in contact with. I would suggest a batten on any side which is against a wall, ie, fixed at a height suitable for the moulded lip, of the bath, to rest upon. On the long side, not against a wall, a suitable frame can be made up to sit under the lip of the bath. This will ensure that there is adequate support when this side has to take the weight of a person entering or leaving the bath. A long packing piece, mounted on the floor, under the bath, fitted so that there is a small clearance under the bottom of the bath, will take, and distribute, the weight, when the bath is filled with water. Paying attention to it's rigid installation, at this stage, will avoid various problems later on.