Using Docker Compose alongside GitLab CI

I am running CI in gitlab with a .gitlab-ci.yml file, I would like to use Docker-compose, as I think it is the best way to get around the multiple image builds in development that I have in my runner. The question is, do I include the docker compose within my CI yml file, or can I keep it separate without a conflict.

Forgive my beginner question, if I could have found a clear answer through googling I would have avoid this.

OS: Linux VM
ComposeV: 1.29.2