When to start using gels and drinks during runs

I have recently started hitting 10 miles on my long runs. I don’t feel overly exhausted and increase one mile a week.

My question is about gels and water while running. Researching on websites has various opinions too and it is difficult to see what is best. Another marathon running friend suggest after one hour runs to use gel packet. I also have no idea what these packets are really.

I am new to longer mileage and don’t want to injure myself. Should I be bringing gel packets or a water belt or something?

What are some basic rules for gel packets or other on the run boosts?