If you're new and bought in during December and now see huge losses... the worst thing you can do is sell now. Prices will increase in the long term. The current dip is just a correction to the wild excesses of last month. Don't panic!
If the prices you can see now are lower than the prices that you bought in at, then the best thing you can do is buy more. Why? This will lower your average entry price.
If you bought bitcoin at $16000 and see it now at $8000, the course of action is clear: buy the same amount at $8000, and your average entry point is no longer $16000, it's (16000+8000)/2=$12000.
Don't sell, buy!