A No deposit bonus is an amount of money that is deposited in a live trading account by the broker for free, it is a promotion that is generally offered by some brokers for new customers who register a new real account. Every client is generally entitled to receive the No Deposit Bonus only once.
I order to receive a No Deposit Bonus, you have to follow the process of opening a new live trading account, fill in an application, verification of your email, verification of your phone number... It is quite rare to have a tradable bonus without verification. The verification procedure is quite simple: all that you need is to upload the scanned copy of a document proving your identity. Sometimes you have to claim the welcome bonus. Then the free welcome tradable bonus is credited to your account, and you can test the trading platform and do some trades. Bonuses are generally credited on a micro account, it is rare to have it on a ECN account. In some regions or countries, an alternate promotion may prevail. Finally, sometimes you have a certain number of days to use the bonus before it is rendered unavailable.
In most of cases, you can withdraw profit but it depends on terms and conditions. Sometimes, you have to reach a minimum profit, or you have to do a certain volume of trades. For instance, the profit shoud be allowed for withdrawal when the trade volume of both buy and sell trades are equal to X lots where X is the total amount of the bonuses received. There could also be a maximum amount of profits that the client can withdraw if they haven't made a first deposit yet.
The bonus is not always withdrawable, it depends on terms and conditions. When it is possible, brokers provide flexible conditions, customers can withdraw bonus funds in case of efficient forex trading. Most of time, you have to reach a minimum volume of trades to make your bonus withdrawable. It could also happen in some terms that bonus could become withdrawable only if you make your first deposit, it is also called payment method verification.