Skype offers Voice over Internet Protocol (VoIP) services that let you call another Skype user for free. If you want to call a friend, but don't know if he's a Skype user, you can search for him. If you find a Skype number for him, he's a Skype user and you can add him to your contact list. The contact list also tells you if he's currently online.
Ask the person if she is on Skype. This is obvious, but it's the surest way to determine if she has a Skype account.
Open Skype and click "Contacts" on the top menu bar. Click "Add a contact" in the drop-down list.
Enter the "Skype Name" of the person's account, if she gave it to you. Otherwise, enter the email address or phone number of the person you wish to add. Emails and phone numbers are unique to a person or family, so any results will be the person's account you want. If you do not see any results, try the person's full name or known variations. If you still do not get any results, then she simply may not be on Skype.
Click "Add" to add a single result to your contact list. For multiple results, click "View" and then click "Add contact" located next to the appropriate result.
Check the left-hand contact list for an icon next to the contact's name. A green circle with a white check mark means he is currently online. A small, yellow "happy face" at the bottom-right of the check-mark, means he is interested in chatting. Any other icon overlaid on the check mark means he is online but temporarily unavailable.