What is the difference between Metatrader Volume and lot size?

I am really confused ,you make orders on meta trader with volume 0.1 ,0.2 until 8. What does volume = 8 means?

Where can I control my leverage?

depends on your broker as to what 0.1 is equal to. Could be 1 mini lot or 1 micro lot.

With most metatrader brokers you have to contact them to get your leverage changed.

NordFX says up to 1:200.

I am really confused. What if I deposited 500$ ,what does trading 1 lot size mean?

You will need to check with your broker as to what your leverage is set at, most likely they set it at the maximum of 200:1. Without knowing your broker its hard to tell what type of account you have. With 500 in your account you need to be trading micro lots or smaller. Although not 100% sure 1 lot is most likely 1 standard lot again check with your broker to be sure.

I mean ,what is the difference between maximum lot and maximum leverage. For a mini-account ,it says max. lot is 10 ? Why specify both ,maximum leverage and lot?

because leverage and lots are two different things. Lot size (or Volume on a metatrader platform) is how much of a currency you want to purchase. Leverage determines how much each dollar in your account can purchase.

1 micro lot = 1,000 of a currency pair.
1 mini lot = 10,000 of a currency pair.
1 standard lot = 100,000 of a currency pair.

200:1 leverage means that for each dollar in your account you can purchase approximately 200 dollars of currency.

Ok ,for a mini lot ,If I had 500$ and I want to purchase 1 lot us$ . Does it mean I want to purchase 10,000$ ? And this means I am using a leverage of 10000/500 20:1??

Another question ,why I can't see profits in pips on MT4? Why I also can't see the price of 1 PIP??

no, 1 mini lot on EURUSD at 200:1 leverage is going to cost your account around $72.00. leaving you with roughly 428 available in your account. You should determine the number of lots you are going to trade based on your risk not how many you can purchase.

You can see your profit as pips in MT4. right click on the window that shows your current trades, select profit and then as points.

Someone probably has an indicator that will show the value of each pip but you can approximate it at around 1.00 per pip with a mini lot. It will be different for each pair but 1.00 is close enough for most.

You can see the pip value when a trade is going on... however, USD-based currency pairs (EUR/USD, GBP/USD, AUD/USD and NZD/USD) have a pip value of $10 per standard lot (or $1 per mini-lot). Other pairs with a different base currency will be calculated in reference to the base currency relationship to the USD. Thus for every other cross-pair the pip value will fluctuate along with changes in rates, while it remains steady for the above-mentioned pairs.

For example, EUR/GBP (where GBP is the base currency) will be 10 * GBP/USD rate while for EUR/JPY it is 1000 / USD/JPY rate, and so on. They are divided where the pair used for the calculation has USD as QUOTE currency (USD/XXX), and multiplied where it has the USD as BASE currency (XXX/USD).

Although there might be slight differences between brokers, you can see an example of the pip values here (scroll down the page to see the table).

As to the "volume", the drop-down list is non-limitative, which means you can enter any other value up to your broker's maximum limit, for example 10 (lots or mini-lots), or 5.6, etc. Leverage applied will influence the amount of margin required on any trade, and is not the same as true leverage, which is related to the amounts of lots traded versus your equity (for example, if you have an equity of $10000 and you open a one mini-lot position, you will be trading at 1:1 true leverage, independently of the leverage applied for the margin by your broker.