XRP is the native token of the Ripple Network - or XRP Ledger - similar to ETH for the Ethereum blockchain or BTC for Bitcoin.
RLUSD is the native Stablecoin of the Ripple Network.
Many are wondering about the connection - both operational and price wise - between Ripple's XRP and Ripple's RLUSD.
Will RLUSD compete with XRP?
This explanation was quite helpful for me

So this is how I understand it: let's say A must send money to B, whereas A and B have different currencies.
If B want $ and A has $, they can use RLUSD.
In all other cases XRP is needed.
Now think of this scenario: A must send money to B in Japan, C in Mexico, D in Vietnam.
Normally A should buy Yen, Peso and Dong.
With XRP instead, A only needs XRP.
The conversion of XRP into the currency of B takes place on B's side i.e. XRP gets converted in Yen in Japan, in Peso in Mexico and in Dong in Vietnam.
Since buying foreign currency entails costs, using XRP is cheaper for A.
Besides, sending XRP is also cheaper (and faster) because transactions on Ripple Network are cheaper and faster than international transactions through banks.