My baby is 3 months old and Im looking into the future of when he is supposed to start solids?

• Should babies eat fruits or veggies first?
• Does it matter?
• Should they be mixed?
• Do they still drink milk when they start solids?

I am not sure when or how to start off introducing solids. I know there is a bit of controversy on when to start, looking for more factual based responses on what baby should be showing in order to move into the new phase of feeding.