Here is a general setup for an outdoor water turtle. You will want to make sure that you have a protective cover or door on top. This is to protect your turtle from predators (like dogs or raccoons) and to prevent them from escaping.
Raccoons are very smart animals and can figure out how to open doors. To prevent this make sure that you keep a lock on the door. You can make the door out of some type of heavy duty screen.
Never use glass or plexiglass! This can cause a greenhouse effect and can cook your turtle. No turtle soup! Fried turtle nor baked turtle!
The basic necessities are to have some type of area where your turtle can get completely out of the water (a basking area), a shaded area where they can cool off out of the sun, and a place to hide.
Sometimes they feel stressed and need to hide from the world. If you have multiple turtles in the same home, make sure that you have a hiding place for each.
In my diagram I have placed an in ground pond (which you can get at most garden centers). For shade you can use some shrubs or even a tree on the outside that will shade part of the area.
They may want to hide in some weeds or tall grass. For the basking area you could use some bricks, wood or cinder blocks. If they have a hard time getting up on the ‘island’ you can place a log where they can crawl up on or make a slope for them to walk up.
I have place a water plant in the water for some food. You still need to feed them regularly. Maybe have some feeder fish swimming with them.