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I am trying to get 18 inch wheels and tires but do not know which kind of tire brand and exact measurements for either. please help

You need to be more specific. What's your budget, willing to roll fenders, lowered car, and general use?

First step is to read the wheel fitment sticky, that will give you a ballpark figure.

Still way to general of a question. Spend some time in the gallery looking and figure out what you like. There is way to many options. If you have no idea what you like we have no idea what to suggest.

which thread can help me understand the measurements and type of tires?

There is literally hundreds of them. The wheel sticky is a good place to start for understand widths and offsets. The entire gallery is full of thread of different peoples builds and setups. It's your car spend some time learning about it and learning about what you like. Then ask a complete thought out question.