Redirection between HP T620 and VDI

We "migrated" our desktop environment to VDI. A third party is hosting the VDI environment.

We have HP T620 thin clients with 4 GB mem

I'm new to VDI. I'm looking for documentation/articles/advise about how VDI works on a Thinclient.

What is redirected, how does the VDI client uses the resources of the TC.

Some users get errors about low memory on the TC's. Does the VDI do some kind of paging?

We also have some blackscreen issues on the VDI. We have open a ticket with vMware.

And some other issues(Keyboard lags/performance/disconnection)

So I would like to know how the VDI interacts with the thinclient.

Thanks