Anyways i can use steam money to purchase games on other website?

No - it's not 'real' money, it's credit towards Steam purchases. The fact that it has a dollar value on it doesn't change that fact. Their TOS explains it as "Steam Wallet funds have no cash value and are not exchangeable for cash."

The money you paid for it is safely in Valve's pockets. What they put in your wallet is virtual currency, created from nothing, you can't compare it to a paypal balance, or a bank account - that means there's no way to get Valve to go paying some external site with your credit as if it was one of those things. All you can do with it, is spend it on Steam in the manner that they intend you to do so, and when you buy games, the devs get their 'cut' straight from Valve.

No, money in your Steam wallet can only be used on Steam purchases

No. Once you have money on Steam, you can't get it refunded back into cash.

So think about it this way: Buy it on the other sites for $17 or $19, or buy it from Steam for $4.

You can buy maybe something for your friend on steam and gift it to them. And then ask them to buy whatever you want from other site.

Better do this with someone you trust though.

For 4$ this seems lot of work,

The whole idea of Web Sites having Special "money" accounts is to keep the money and earn Interest on the "Free Loan" it provides.

Gift Cards,

Sony' PSN store, ($5US blocks)

Steam money,

etc. They take your money and eventually provide a sale meantime hoping you will forget about the money while they accrue sizable interest on the "free loan" of your monies.

Your money is also Locked into their Specific store. The idea being to keep you from buying at other Vendors shops.

Nope.

is it on your card or from a gift card. if it is from a gift card then no.