Where do I put my fingers on a cello?

Your index finger is called 1, your middle 2, your ring 3, your little 4.

When you play a string with no fingers, that is called "open"

When you play open 1 3 4 it should sound like DO RE MI FA

If you do that on two strings in a row, you get a major scale.

Marking the spots is common but can be problematic.

You cannot see your hand unless you distort your posture, so make sure you only use it when you set up. Don't learn to play with your head turned all sideways. Or you can use a mirror.

Also take time to learn the bow and the fingers separately before you try to put them together. (Pluck the strings to learn the fingers)

Also.. You know.. Get a teacher.

Overall, self teaching doesn't work so good.

You wouldn't teach someone else to play an instrument you don't know... So why different logic for teaching yourself?

No one can tell you where to put markings via a message board. There are slight differences from one cello to the next, differences that are significant enough to make the note sound out of tune.

Cello is really not a self-teaching instrument.

First, tune your instrument. Then, put your finger on the string and move it until you get a sound one full step higher. (One full step is the difference between "Do" and "Re"). Mark that spot. Then, find one full step above that ("Mi") and a half step above that ("Fa"). With those markings, you should be able to figure out some major scales and work your way through your first-year book. If you don't have a book, go to a music shop and ask for an essential elements cello book.

If the instructions I gave you aren't good enough, you need to hire a professional to give you lessons.

You are already experiencing the principle problem of 'teaching yourself' to play the cello - you're learning from someone who knows nothing. Not only will this prevent you from making meaningful progress, you might even injure yourself in the meantime, ending your playing enjoyment before it has even begun.

Get a teacher!

I know where they are if. I were there I would help you. haha. I would suggest youtubing it.