This information will be in the manual. Briefly, aim the camcorder at the subject, and press the record button. Not knowing the make of the equipment, we cannot help with the second part of your query.
You have given no information about the equipment you are using, the connections, the software and the OS on the computer. Not knowing these, we cannot begin to offer any guidance.
This could be either a bad viewfinder or a bad CCD image sensor. Neither of these are user serviceable and will require repair by a qualified repair shop.
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Very often these older camcorders have internal batteries that give out so you need to plug in the power card and that should at least let you use it using the charging system. It may take awhile before some juice is picked up by the old internal battery and then try it. You may be able to buy a new rechargeable battery for it on eBay.