@Colton20 4 guests means the listing can accommodate up to 4 guests, no more than that. Some listings charge a set price for up to the maximum amount of guests, no matter how manypeople are on the reservation, but it's more common to charge a certain amount for 1 or 2 guests, and then there will be an additional fee for each guest over that amount, but it's usually not much- it covers the extra costs the host has in utilities, amenities, laundry, etc. for more guests.
When you book a place, you need to enter the correct number of guests, no matter what the maximum allowed is- you can't just book it for 1 and then show up with 2 or 3 more people. The host has the right to refuse entry to anyone not accounted for on the reservation, and it will lead to a bad review for you if you try to do this.
The way you determine whether this is a shared home listing (other rooms in the house rented to other guests) is by thoroughly reading the listing description. If it says "Entire house", that should mean you have the place to yourself. If it says "Private room", that means you are only booking a room in a house and could be sharing common spaces with the host or other guests. If a listing is unclear to you, use the "Contact Host" button to ask any questions you have before booking.