You will know when your room selection time opens up through your Housing Checklist on the Campus Portal.

When the link becomes available - click on "Click here to choose a room."
Select the session that you are selecting a room for and review the warnings. When you are done reviewing, click on "Browse Rooms"

The room selection tool allows you to search for a specific building, pick a room, filter through max capacity, show only the remaining room slots etc. You can also click on the room name to see more details about the room. There will be a photo of what the room could potentially look like - while it may not be the EXACT room - it shows a basic layout of the room.
You can also see the "Remaining room slots" to see how many people have already selected that space.

Once you select a room, you will receive a confirmation message:

If you confirm your selection, there are no changes made until one week AFTER you move in. This is your room that you will be moving into for the next semester, so be absolutely sure that this is the room you want.
After confirming your selection, you are ready for move in!
Keep an eye on the Housing Dates and Deadlines Article for when your move in date is.