Do a search, it's been discussed many times.
Briefly:
* FAA Class 1 medical
* CPL theory exam
* CPL flight test
If you do the test in a s/e a/c then you will have Commercial Pilot privileges valid for s/e a/c only. If multi then Commercial privileges will be valid for multis only.
To get both s/e & m/e requires two separate flight test although if you do them with the same examiner etc s/he may let you off repeating some common items.
To gain instrument privileges:
* IR exam
* IR flight test.
Usual caveats about s/e IR not being valid for multis - I think.