The factors of 121 are 1, 11, 121. Here is how you calculate the factors of 121. The first two factors - and sometimes the only two - are the number itself, and 1.
Try 1. 1 x 121 = 121, so put these into our factor list.
1
...
121
Take 2... no good. 121/2 isn't a whole number. So we skip 2.
Now take 3... no. 121/3 isn't a whole number. So we skip 3.
Next try 4... no luck. 121/4 isn't a whole number. So we skip 4.
Now try 5... nope! 121/5 isn't a whole number. So we skip 5.
Try 6... no good. 121/6 isn't a whole number. So we skip 6.
Take 7... no. 121/7 isn't a whole number. So we skip 7.
Now take 8... no luck. 121/8 isn't a whole number. So we skip 8.
Next try 9... nope! 121/9 isn't a whole number. So we skip 9.
Now try 10... no good. 121/10 isn't a whole number. So we skip 10.
Try 11. 11 x 11 = 121, so we add it to our list of factors. There are no numbers between 11 and itself, so we can stop.