i think this is what we do if we want to make high profit, but for the simple learning, i think you can select in any altcoin in market exchange, buy it when the low price is reach and wait until the high price you want for selling that coins.

how we know the low price? we can watch the movement for selected coins for a while, maybe for one until three hours before we decide to buy and if we are sure that coin is really in down price, we can buy for small amount first to test, and see the market movement, is it really down or is it go up.