Either you replace your wired device with a WLAN router or you simply connect an wireless accesspoint to your wired device.
Accesspoints are auite easy to handle since they just "spread" your connection from the router. Most of them can be configured to search for the correct settings themselves (dynamic IP).
Assuming your wired to wireless connection is built up, you need an wireless receiver for your PC. They come for several interfaces (USB, PCI, etc.).
You then can connect the PC with the WLAN.
I know this is very simplified but does it answer your question?
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