I have Mikrotik RouterOS v4.14 with hotspot DHCP have the same pool.

I notice that in pool you can have range of IPs instead of 1

Is there a diffrence between spesify the pool with the ips
192.168.1.2-192.168.1.254

and have a three ranges:
192.168.1.2-192.168.1.100
192.168.1.101-192.168.1.200
192.168.1.201-192.168.1.254

?

what about have different pool?
I mean having those above ranges as different pools and set the second pool as next pool to the first
and the third pool as next pool to the second one.

ex:
Name :pool A
addresses: 192.168.1.2-192.168.1.100
next pool: pool B

Name :pool B
addresses: 192.168.1.101-192.168.1.200
next pool: pool C

Name :pool C
addresses: 192.168.1.201-192.168.1.254
next pool: none

or even more pool, I saw some people having this. Does this make difference in the speed of getting an IP ? Is there other diffrences?

I have Mikrotik RouterOS v4.14 with hotspot DHCP have the same pool

Hotspot doesn't need a separate pool unless you specifically intend to make use of the Universal Client feature. /ip hotspot universal is the same as using /ip hotspot address-pool=.

I notice that in pool you can have range of IPs instead of 1

Were you previously declaring pools with only a single IP (/ip pool name=pool1 ranges=192.168.1.2) ?

Is there a diffrence between spesify the pool with the ips
192.168.1.2-192.168.1.254

and have a three ranges:
192.168.1.2-192.168.1.100
192.168.1.101-192.168.1.200
192.168.1.201-192.168.1.254

The former utilizes almost a single /24 and keeps all hosts on a single layer 3 subnet.

The latter obviously splits up the hosts between a few layer 3 subnets. Any communication between hosts on the different subnets will have to pass through the router. If you have a lot of intra-subnet traffic, and no desired traffic filters, this is wasteful as it will result in inefficient use of your RB's NIC. It'd be better to keep the hosts a single subnet.

what about have different pool?
I mean having those above ranges as different pools and set the second pool as next pool to the first
and the third pool as next pool to the second one…or even more pool, I saw some people having this. Does this make difference in the speed of getting an IP ? Is there other diffrences?

This makes no difference other than what I mentioned above. Stay away from this unless you have a specific reason such as that mentioned above or you're wanting to distribute IPs from several separate public IP blocks.

I actually don't want users to communicate with each there but for that I set the DHCP netmask to 32 and I have one range pool from 192.168.1.2-192.168.1.254 (192.168.1.1 is for hotspot page)