I cut a few slices into each tube so I could fold the edges to create a bottom.
The Pinterest posts I saw promote how the tubes would decompose and the plants would be ready to go directly into the soil. That's not the ideal seed-starting situation. Really, once seedlings grow their first true leaves, it's best to re-pot them in garden mix to they can continue becoming strong before they live outdoors. Also, the tubes are dry, porous material, so they will wick water away from the soil in inside - robbing the seeds of moisture. It's true the tubes disintegrate quickly, so it's best to use twine - I used rubber bands - to secure them before dipping them into a bath to moisten.
After a quick dunk for the tube, stuff it with moistened seed-starting mix. Plant seeds according to depth recommendations on the label. I use craft sticks for seed-starting because they also double as a dibble - to make a hole for each seed. I move the stick to the edge as a label.