It's in the TurboActivate package on your API page. You must be logged in to get it (sign up if you don't have an account). It's all explained in the Using TurboActivate with VB.NET article.
Tell me if this helps.
turboactivate in VB.NET
See the Custom license features article. In short, you need to create a custom license feature, then when you create a new product key (or edit an existing key) the feature field will be there. Just enter the value you want.
To use the feature in your app use TurboActivate.GetFeatureValue()
kumarPlease give the sample code using the functions UseTrial(), TrialDaysRemaining(), and ExtendTrial() for offer timed trials in vb.net
We'll include a full example of using trial functionality in the next version of TurboActivate (we're trying to get it out by Friday).
That being said, the trial functionality is pretty simple. FIrst check if your user is activated (TurboActivate.IsActivated()), if they're not call TurboActivate.UseTrial(). Then, immediately after UseTrial(), get the number of days remaining to see if they can continue using your app (use TurboActivate.TrialDaysRemaining(), obviously).
If you also want to offer trial extensions, you can put a button on your form, or in a menu, when your app is in trial mode. This button will launch a new window with a single textbox where they can paste the trial extension key. When the user clicks "OK" on the textbox you can use TurboActivate.ExtendTrial("pasted key") to extend the trial.
Does this make sense?