Summary:
1. Create a new VPN Topology (think this as if community in Check Point)
2. Config IKE
3. Config IPSec
4. Create Rules
5. Save and Deploy policy
1. Devices > VPN > Site to Site > Add VPN > Firepower Threat Defense Device > Fill out the "Topology Name", choose "Point to Point", Node A: <local gateway>, Node B: <peer gateway>

Local Gateway:

Peer Gateway: repeat the same process above.
2. IKE

3. IPSEC

4. ACLs
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Policies > Access Control > Access Control > click the policy name to edit
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Rules > Add Rule > NOTE: you will need to figure out Source and Destination Zones (see below)

Identifying Zones:
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Essentially, Firepower is a Cisco version of ASA, so you can figure out zones via packet-tracer via cli.
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SSH to the gateway, you will see ">" prompt. You can change it to "#" by typing "system support diagnostic-cli"

5. Save and Deploy policy