When two people have been living together and they decide not to live together anymore, they are separated.
When married parents separate, their marriage is not yet ended. They have to get a divorce to legally end a marriage.
Parents who separate often make a separation agreement that states who their children are going to live with and how they are going to divide their property. A separation agreement is not the same as a divorce, but it is a contract, which means that both parents sign it and then are bound to do what they have agreed to.
In the vast majority of cases, children get to spend time with both parents. How much time you spend with each parent, and exactly how that will work, will depend on your custody and parenting time (visitation) arrangements.
Remember: Parents divorce each other, not their children. Your parents are still your parents, and they still love you.
Parents who never married or chose to live together without getting married—don't have to get a divorce, because there is no marriage to end. But they do need to decide what will happen to their children and how they will divide their property.
In some cases, your parents will make the decisions together about who you will live with and how that will work.
Whether your parents make the decisions about custody and parenting time (visitation) themselves, or with the help of a mediator or a judge, your opinion may be taken into account.