Lay out the the fence line with a measuring tape and wooden stakes. Run a string line between the stakes to mark the fence line. Once the string line is complete, make sure it is square. Now mark your on-center locations for the corner and end posts, then mark your intermediate post locations.
Dig holes 24 inches deep and 18 inches around. Gate posts need to be set with a larger footing since they get yanked on continuously during their lifetime.
Set your posts into the holes one at a time. Set a fence panel on the ground nearby so you can use it to ensure you have the posts set the proper width apart.
Each time you set a post, use quick-setting concrete to fill the hole. Fill the hole with concrete until it is 4 inches below the ground level. This will allow you to pile dirt over the concrete footing and conceal it later. Use a magnetic level to assist you in plumbing and leveling all of the posts.
Return to posts you have previously installed as you go to check their plumb and level. Straighten them as necessary. You need to stay on it so the concrete does not set up on you with a post out of plumb and out of level.
Insert aluminum panels one section at a time, once the concrete has dried. This is usually like an erector set process and requires the nuts, bolts and screws that the fencing company provides.
Once the main fence runs are in, install the gates.