As mentioned, there are different methods and learning styles for memorizing the layout of your cello fingerboard. Some people find it easier to conceptualize where the notes fall for each position, while others prefer to memorize the distance between the positions and feel that out while they play. This is something that will take lots of time and practice. Some students and beginners prefer fingering tape like thin graphic chart tape to mark where their fingers should play along the fingerboard. This type of tape won't damage the fingerboard and can be removed once you have memorized the layout.