Mike

And you were told right. A guide bushing can be made from plastic, brass, aluminum or steel. It attaches to the bottom of your router or to a mounting plate if the router is in a table. The size of the bushing determines the offset: all this means is how far away from the template. 1/2 the size of the bushing is the offset. How to select the proper bit and bushing combination is explained in several posts under guide bushings and templates so I wont repeat it here. Most routers do not come with guide bushings but they are readily available in stores. A bearing is just that, a roller bearing mounted on the router bit, either above or below the cutter depending on the application. Bearings that are end mounted are often removeable so you can get additional uses from the same bit. There are also bearings that slide onto the bit shaft and are held in place with a collar. Most are round, some are square and they all work. Again you can read about the differences elsewhere in the forums.
There is no need for an expensive guide for box joints. The Oak Park box joint jigs are super simple and get great results. They are made from quality HDPE which lets the wood slide like a dream. They also have about the fastest set up of any brand on the market and cost just over $20. You can make your own but this is money well spent.

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Mike