How many 4 digit numbers can be made out of the numbers 0-9 and what are they?

Assuming several things:

Numbers can't start with zero;

Repeated digits are allowed, then:

First digit can be any of 9,

Second digit can be any of 10,

Third and fourth digits can each be any of 10;

There are therefore 9 x 10 x 10 x 10 ie 9,000 possible answers, which by coincidence is the total of the numbers from 1000 to 9999.

If howerver you did not intend to allow repeated digits then the first digit can be one of 9, the second also one of 9 (zero now allowable), the third can be one of 8 and the fourth one of 7, giving a total of 9 x 9 x 8 x 7 ie 4536 arrangements, some of which will contain the same four digits but in a different order eg 1234 and 1243. If you don't want this then divide by 24 and get a more manageable 189.