I know carbon cant make MORE than 4 bonds, but can it make less?

Carbon must always have 4 bonds - not more - not less. In the case where you say:" Another has 3, one to another C one to an O and one to an H." The problem here is that the bond between C and O should be a double bond C=O . This will satisfy the 4 bonds on the C and also the required 2 bonds on the O. If it is shown as you describe, then it is not correct.