I read some articles about leverage but I am not sure I understand about it. I think:
example: EUR/USD = 1.25628/1.25647 and I want to buy 100,000 EUR ( standard lot), I have to use 100.000*1.25647 = 125,647 USD. If leverage is 100:1, I need 125,647/100 = 1,256.47 USD to trade.
Is my opinion true? Thank in advanced!
Exactly 
and if your account equity dropsbelow this… Then your broker will close the position… This is what is known as a “margin call”
Thank you very much!
Assuming that I have 2000 USD when I trade, when does “margin call” appear?
If you only have $2000 to trade, and you are trading 1:100 leverage and are using a standard lot… You would be able to sustain roughly a 75 pip loss before margin call.
Do not trade a standard lot if you only have $2,000 in the account. Use a mini lot of $10,000.
In my example, 1 pip = 10 USD , loss 75 pip = loss 750$, 2000 USD - 750 USD= 1250 < 1256.47 => margin call. I understand, thank you very much!
to be more conservative, hoctrade can trade micro lots with his $2,000 account
Leverage is a boobie trap created by brokers to suck out your money faster and charge more spreads. If you make a good money management you will not need leverage. 1:5 leverage is a little excesive for me, i risk less than 1% per trade.