your rear brakes are self adjusting to a point, and yes the parking brake is adjustable as well.
here is a video not a great one but it gives you the basic idea of how to adjust the rear brakes.
https://www.youtube.com/watch?v=ooqwmy7nfzo#action=share
with your rear brake self adjusters they just keep the brakes in the ball park.
This is provided everything else is in order, meaning your springs should be in good shape, if they are worn with missing or flaking paint the spring kit should have been replaced with the last brake job.
The threaded adjuster needs to be cleaned and lubricated the entire length of the threaded shaft with anti-seize this is normally done.
The backing plate friction points where the shoes ride on the backing plate should be clean and lubricated with anti-seize.
the guy in the video is promoting chlorinated brake cleaner, Chlorinated brake cleaner has chlorine in it along with other chemicals which can severely rust non coated non lubricated parts. so this is a bad idea in my opinion.
if your brake drums are out of round or worn with a rust lip at the edge of the brake drum where the shoes do not contact the drum, getting a properly adjusted rear brakes will be a little more difficult or impossible.
With out of round brake drums once you get the shoes adjusted up better than they are now, you will feel brake pulsation more.
It is critical that your rear drums are like new they should be machined or replaced if necessary.
Most cars have rear brake adjustment windows in the backing plate that are used to properly adjust the rear brakes while the tire is mounted to the car.
Some cars you can use a screw driver to adjust rear brakes others you will need specialized tools for this job.
When the brakes are adjusted properly you should be able to spin the tire not more than one revolution, this is tested with the tire on the car on just spinning the drum like shown in the video.
the adjustment for the parking brake is done after the rear brakes are good and adjusted properly.
if I remember correctly you should be able to pull up on the parking brake handle 3 to 5 clicks or 1/3 of the total travel before significant effort is needed to raise the handle any higher.
while pulling up on the handle one click at a time and the car up on jack stands, check the resistance of each rear wheel they should grab evenly, requiring the same effort to rotate each tire.
if one is easier than the other you may have a seized or stretched cable.
By the time you get the handle raised to a normal amout of effort you should not be able to move either rear tire at all.
This is a parking brake, not a emergency brake. it is not designed to stop the car when under power or blasting gown the road.
A parking brake is to make sure the cars weight does not put excessive force on the transmission when parked and to make sure your car is where you left if when you parked it on a hill.