Since no one has taken a 'shot' at answering your Post, I will.
I have a personal preference. I use a Latex-based Sealer. I use the type with Sand already mixed in. The Sand will 'fill' gaps in the asphalt that are 1/8" or less in width. I don't roll my Sealer on - I 'broom and squeege' it on.
There is a broom & squeege that you can buy at the Home Center. I suggest you power-wash the asphalt first. Let it dry for a day or 2. (DON'T do this in the height of Spring Allergy Season. Do it in August or September.) Read the container carefully to be sure you can do the job in the right 'conditions'. You want hot days in a row. Start early in the morning. Make sure you mix the contents regularly because the Sand Sealer settles out fast! $10 on up is a good price for a decent Sealer in SE PA.
If you have more specific questions, you know where to find me. My best to ya and hope this helps.