First time mom

Ok im a first time mom and I have a son that just turned 4 months and im expecting another one in april. Anyways I was wanting to know when do I take my 4 month old son off milk and start feeding him baby food?

You don't take them off milk- you add the baby food and STILL nurse/formula feed. Talk to your child's pediatrician about how to introduce baby food. Providing your son doesn't have any medical conditions, you can probably start feeding him a little bit of rice cereal (made with breast milk or formula at first) now. They recommend starting them on vegetables first because they're less likely to eat veggies if they've tasted fruits first. My son's doc suggested I go by yellow foods, add green foods, and purple foods, then add red foods because they seem to have less issues with things that way as far as allergies/constipation go.
My number one bit of advice for you would be to contact your son's pediatrician- they answer questions like this daily.

you can start him as early as six months on first foods. he will still want a bottle afterward, but you can start giving him rice cereal now. and next month or a lilttle later try first foods baby food! have fun!