Explanation:
PPTP (Point-to-Point Tunnelling Protocol) is a method for implementing virtual private networks. PPTP uses a control channel over TCP (Trasmission Control Protocol) and a GRE(Generic Routing Encapsulation) tunnel operating to encapsulate PPP packets, the purpose only on implemented security functionality. From the figure above, you can choose to enable or auto enable or only use PPTP to connect WAN network.
(source: https://en.wikipedia.org/wiki/Point-to-Point_Tunneling_Protocol)

Explanation:
There are three types of encryption which are no encryption, stateful encryption, and stateless encryption. Stateful means the computer or program keeps track of the state on interaction, usually by setting values in a storage field designated for that purpose. Stateless means there is no record of previous interactions and each interactin request has to be handled based entirely on information that comes with it.
(source: http://whatis.techtarget.com/definition/stateless)

Explanation:
Distant Segment and Netmask can choose to disable or enable. If enable it, the distant segment and distant netmask is need to fill in because as networks grow to increasing number of segments, more network address numbers will be needed as each segment requires an individual number. So, that why we need to put the number. The interval is the time between two points. The retry is the number of attemps if there is any failed. Default IP Segment Range is between 192.168.1.128 until 192.168.1.255. So the IP Segment Address and IP Segment Netmask should be in the range.
(source: http://www.networkcomputing.com/unixworld/tutorial/001.html)