Yes, bicycle shops generally provide repair services. A typical list of offered services includes regular service/adjustment (including safety check; and brake, drivetrain, and tire inspection); premium, and annual service, which is a more extensive tune-up. More specific repairs include drivetrain tune-up, brake system tune-up, flat tire fixes, brake repairs, cleaning and touching up the bike frame.
There are two major types of headset- older, threaded headsets that have a quill that drops into the stem of the fork creating an interference connection, and newer threadless headsets that the stem is bolted and clamped on to. Flat handle bars are preferred by off road cyclists who can ride in a more upright postion whilst still having the controls at their fingertips, whereas drop handlebars offer more cycling positions and are favoured by road cyclists who typically spend more time in the saddle. The controls attached to the different styles of bar are operated and maintained in different ways.
Whether you ride a single, 7, or 10 speed bike or anything in between, you will need a slightly different chain. The major difference is that they come in varying widths to accomodate the different spaces between the gears, but quality of construction is also a factor in choosing a chain. Inspecing the chain should be a part of your regular cycle maintenance procedure- It’s important to keep a chain well lubricated, but oil will also attract dirt and so different oils for specific riding conditions are available. Remember to clean your chain regularly to get the longest life out of it and the gears.