A couple questions from a beginner.

I'm going to brew my first batch. It will be an extract clone of Sam Adam's Summer Ale. I am not using a secondary. The primary will be in a chest freezer/kegerator where the temp can be properly maintained.

1) How long should i leave it in primary fermentation?

2) What is the best way to carbonate using a corny keg?

Thanks

1) at least 3 weeks. 4 is better. Allow the yeast time to do all their work.

2) I don't keg so I have no advice here.

I usually primary for at least three weeks. Rather you choose to secondary is then your decision. Not sure there is a best way to carbonate a keg. I choose to set the psi at serving temperature and wait three weeks. But there are other ways that get you there too.

https://www.homebrewtalk.com/f35/keg-force-carbing-methods-illustrated-73328/

i'm not sure i want to force carbonation.

For most of my beers I ferment in primary for 3 weeks and then transfer it to the keg and set it to my serving pressure (about 12 psi) and let it carb/condition for 2-3 weeks.

do you use any priming sugar?

There is no set amount of time for fermentation let gravity be your guide. after a couple weeks take a gravity reading, wait three days and take another. If it has changed, wait another three days. if it has not changed and it's more or less at the gravity you expected it to finish it is finished.

if you do not want to force carb in the keg you prime with sugar just like in a bottle but less. Find an online carb calculator or use a brewing software is easiest but as a ROT, depending on style around 3-4 oz of table sugar should do the trick, you will still want to hit the keg with a little co2 to make sure the lid seats well.

to force carb I set it at service preasure and rock the keg back and forth until no more gas goes into the keg (you can hear it hissing) or until I get tired. Then leave it for a couple days.