Ok, slow down a moment...
Usually, the install is just the reverse of the removal.
The core slides into that gap, with the hose tubes going to the front firewall/bulkhead - did you manage to save the original seals? Because those seals are what helps hold this core while you center and fasten it.
See number 5 in the graphic? That mates with the seal #4 - the tubes slide thru those holes - #18 them bolts to the housing with a few screws - you have a seal on the unit itself - thats ok, the seals I'm referring in #5 and #4 are the ones that go where that lights' shining in...
What's up with that torn plastic?
It's obvious they tore it apart.