Is your camcorder tape-based or file-based? If tape-based, you need a firewire cable connection. If file-based, you can use USB.
Also, is your camcorder analog or digital? If analog you will need first to convert the video to digital with a digital converter. If it is already digital you should be able to play it straight trough with just the proper cable connection.
Some camcorders are not compatible with importing directly into iMovie. Check the Apple website link below to see if your camcorder is listed as compatible. Pretty near all tape based camcorders are compatible even if they are not listed.
https://support.apple.com/en-us/HT204202
-- Rich