BGP is formed on unicast ipv4 address

Networking
1

So when they say BGP is formed over unicast IPv4 address they mean this ?

R1
config t
router bgp 100
neighbour 2.2.2.2 remote-as 200
end

R2
config t
router bgp 200
neighbour 1.1.1.1 remote-as 100
end.

Meaning I explicitly mention the neighbour I want to form bgp peering with ?

2

and these ip adddress must be reachable? thats what it means?