There are various ways to do this. We'll use continuous division by 2:
1000 ➗ 2
500 rem 0
250 rem 0
125 rem 0
62 rem 1
31 rem 0
15 rem 1
7 rem 1
3 rem 1
1 rem 1
Starting at the end we write the final result (always 1) followed by the remainders in order:
11111010002=100010