This option can activate your license if you run LEX in the trial and evaluation mode and have just purchased a license. In the purchase process, there was your license file sent to you, so that this is the dialog where you should give the complete path to the license file:
If the License is correct, then you can use LEX without any limitations:
You can download and use LEX - The LDAP Explorer without purchasing a license: This is to give you a chance to test the application in your directory environment extensively. However, there is a functional limitation in this trial and evaluation mode: You cant see all the objects in the object list, nor edit, nor export them:
If you run LEX in the trial and evaluation mode, this is indicated to you at every program start. You can activate a purchased license right here, also (by using the Activate Existing License button).