Bitcoin or Altcoins trading you need investment to buy some coins low and sell when the price is high. Even in basic buy/sell trading require basic knowledge of trading which is needed to to determine when to buy (entry) and sell (exit). Alternatively you can participate in some airdrops, signature campaign etc. Those are free coins but moreover you still need to wait for you to sell it. In campaigns you are paid by your effort but i think much higher rank is need on this.