how can do floor and ceil function in MIPS assembly?

You should definitely get some copy of the MIPS instruction set reference. Even without that I was able to find the instructions floor.s and ceil.s using Google.

However, these are only supported with newer MIPS CPUs. But you can also do it the hard way by adding or subtracting 0.5 (depening on the sign of the argument and the function) and convert the result to an integer.
[EDIT]
And Google will even find an example for floor: https://github.com/jrvidal/goruden-boi/blob/master/lit/cs61c/floor.s.md[^].