1st : What gives Altcoins value and make traders trade in them? Is the company of an altcoin invent it and start mining and put the coin in trading sites and that's all or what? no real investments and trading in real life?
most of the altcoins that i trade are those that have a good future, a good dev and most important of all the community support.
and the price is only supply and demand and nothing else.
2nd : People say buy when price is low and sell when high, so why don't smart traders buy very big amont when price is low and sell when high and earn lots of money? for example, buying a coin with 10 BTC amount and sell when price up 15% = earning 900$ !
for that you will need a time machine to go to the future and see which price is low and which is high.
and by all means if you trust a project enough to invest $6000 in it and take the risk then invest and take the reward but only if you are willing to take that risk!!
3rd : How to trade in altcoins with knowledge of when the price will get low or high? I started trading with small amounts but i'm like buying and selling with just "Guessing". I mean in real life, country's economy and Imports/Exports control in its coin value, so in Cryptocurrencies just trading "Buying/Selling" the coin control in its price or what?
it is not guessing, it is mostly speculation based on the analysis that you do in each market when seeing the history and also seeing the market and how people are reacting to it.
and yes in cryptocurrencies only buying and selling also known as supply and deman controls the price.