Grocery store/running errands advice

I currently live upstairs, in an apartment. My car is not close to my house. My baby is 6 weeks but I have not run a single errand unless my husband has been home or gone alone. I’m not sure how I’m supposed to buy items, and bring the baby back to my apartment and hold all the stuff we need. Any advice? What do you do? I don’t want to leave the baby sitting in my apartment while I walk back and forth to my car for items. What does everyone else do? If you have a house, do you park in the driveway and leave the baby in the house while you bring in groceries?