It is not necessary to soak steel cut oatmeal before cooking, but it is optional. Soaking steel cut oats will soften the oats and also make them cook more quickly. Thye also tend to have a fluffier, creamier texture when they are soaked beforehand.
To soak oats, simply cover them with water and let them soak for at least one hour, ideally overnight in the fridge. Strain out the water before cooking.