A tidally locked planet does not rotate in relation to its sun. One side is always day, one, always night. This is caused by tidal forces pulling all planets towards this same equilibrium, so it’s completely stable once it does occur…a tidally locked planet at an earthlike distance from the sun would be scorching heat on one side, freezing ice on the other.
What about at different distances? Is there a band of orbital distance where the night side of a tidally locked planet is warm enough for liquid water? Or one far away enough that the day side can have oceans?
I think they would be hard for life to naturally develop on this kind of planet, the winds would be very strong and the water would be always running away from the day zone to precipitate on the night as ice, so even the twilight zone would be hostile to life.
But colonization is a possibility.