It's called EMLA and it's the same cream used for children when a general anesthetic is needed. It's aka 'magic cream'.
When I had my tattoo done I the tattooist asked about using this cream and was advised that it's quite possible the cream only numbs the top layers and therefore doesn't do what you want it to but can actually make it more painful because it's more a concentrated pain
I didn't use the cream and in all honesty after less than 30 seconds it really wasn't painful at all until he went over the bone, that did hurt but was bearable
If you decide to use it, then you can of course, use it at any other sittings you may need but you will need a largish amount as it comes in quite small tubes and costs around £5 per tube.