Trying to sell some coins with high gains to buy some that has dipped alot, but it seems they all move up and down together for the most part. This makes it hard to sell. Is this how it normally is? Been trading just a month now.
Of course not, they have different fluctuations depending on the 'large or small' number of 'users or investors' behind it. In the case of a 'mutual' decrease or increase, this is usually due to sales, and purchases occurring simultaneously on each cryptocurrency or possibly a simultaneous closing of cryptocurrency exchange accounts in a country.
They have different fluctuations when the market is relatively stable, but once Bitcoin starts dropping significantly, you'll see that the value of pretty much all altcoins is tied to the value of Bitcoin.
That's not to say that you can't make a decent profit of of altcoins, like you said, there's a big difference in how much they fluctuate.
I also wouldn't say that the parallels between BTC and alts are due to buy or sell orders happening simultaneously, that's an effect, not a cause.
If the Bitcoin value drops, altcoins also become less valuable since they are traded in Bitcoin, thus their value in fiat also drops.
Go check the BTC charts on coinmarketcap, you'll see a different picture.