I now have $ 500 in capital. Is this the right time to hold the coin. and what kind of coin should I hold? I need some advice now, Because according to my judgment this will be the momentum for altcoin to explode in the end of 2018
I would advise you to hold bitcoin if you dont have any. Holding at least 80 percent bitcoin is wise, at least for me. Trade if you must to, but be careful. I like monero as a one of the few good alts.
Bitcoin is of course the safest option, but it won't give you 100X as the right alts could give if you are able to pick the right ones. Some coins like DeepOnion have lost almost 99% from ATH, they could be an exciting gamble.