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You need adapters to comnnect your PEX piping to the new fixture. Since y probbaly don't have a crimping tool for the PEX rings your best bet is push lock ("Sharkbite") adapter fittings
The link below is a typical Sharkbite adapter. You simply push the PEX into the fitting and it locks in place. That's all you have to do to make the connection.
Bear in mind that the adpater linked above may not the the correct size since there's no way I can tell from your pics what the size would be. The PEX looks like and most likely is 1/2" but the threaded connections I can't say for sure so bring the new valve/fixture to Home Depot or Lowes to get the right adapter. Tell them you have 1/2" PEX.
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