This for using where clause :
UPDATE employees SET gender = 'Male' WHERE id IN (1,2,3)
If you want update all rows in table then:
UPDATE employees SET gender = 'Male'
You can use the same thing, but for the ID's you can use ID's in
.... where id in (1,2,3);
You can also write a nested query inside IN.
For more details on how to write IN you can refer here.