I was in a captains meeting a couple of years ago and they provided a basic of show the calculation works.
If you play singles, your full Usta rating, ex 4.06 is compares to your opponents rating, ex 4.18. They consider every .06 of difference to equal s break of serve and compare actual result to this. So in the example, the result should be, 64,64. If you win 76,76, they take the result number of breaks against expected. In this case, the difference is .12. They will take this number and divide by 2, and adjust both individuals by this amount. So after match, your new rating is 4.12and your opponents is now 4.12.
In doubles they add your rating and partners rating together for your team and do same for opponents. They then do the same as for singles with expected score and result. Both partners will adjust by the same amount so the difference between you and your partner will be the same after match as before.
Now how the other items like benchmark, your actual full rating, anything with tourneys, mixed, etc in the mix.
Hope this helps.
