It does have fragmentation in terms of location of the data, but its not important at all since access time to any block is really quick.
With typical magnetic HDD access time is determined by speed of mechanical parts like headers and rotational speed of the magnetic dish and that makes a whole difference. HDD header has to move from point A to point B, longer the distance longer it takes, The best is that all data in the reading sequence lay down on the same track so actually header doesn't have to move at all. So generally defragmentation makes that all small portions (blocks) of one file are keept as close to each other as possible so this reading sequence is optimal.
I'm not gonna mess your mind about that, most people doesn't run defragmenation anymore because it takes quite some time and at current technology of HDD's only enthusiast/professional users will notice the difference. But thats something to keep in mind when you feel HDD gets sluggish in reading data.
"SSD only have 1 type/size correct? (not sure if there is 2.5 and 3.5 like the normal spinning hard disk)"
Yes and no, most of them have typical 2.5" size, but remember there are models which can be connected to M.2 slot or PCIe so will look different.
2.5" size is most common since SSD's primarily was made to fit in laptops instead of typical HDD's, due to it's lower energy consumption...