I'll explain using the output from one of our PPP interfaces, which is a DSL connection:
ppp10 Link encap:Point-to-Point Protocol
inet addr:18.104.22.168 P-t-P:10.1.48.1 Mask:255.255.255.255
inet addr is our local IP address (inet indeed stands for Internet). If this isn't the case for you, there must be some NAT somewhere, or other weirdness.
P-t-P is the peer's IP address. Doesn't have to be routable (and this one isn't). The peer no doubt has multiple addresses, one of which is probably routable.
Mask is the netmask. A PPP link is a point-to-point link, so it's /32. The only thing on the other end of the link is the peer. (You may think the entire Internet is there, but it's not, you have to use the peer as a gateway.
ip route ls will show the default route via the peer—on your system, our routing is more complicated.)
UP POINTOPOINT RUNNING NOARP MULTICAST MTU:1492 Metric:1
These are the interface flags. It's up, it's a point to point link, it's running (I'm not sure this is any different from up for ppp). It does not use arp (no surprise, it's not Ethernet). It passes multicast traffic. It has a maximum transmission "unit" of 1492 bytes (because this is PPPoE). The metric is 1, which is used by some dynamic routing protocols.
RX packets:92800 errors:0 dropped:0 overruns:0 frame:0
TX packets:93810 errors:0 dropped:0 overruns:0 carrier:0
Only interesting thing here is the RX/TX count. I suppose errors and dropped are possible, but haven't occured.
RX bytes:12597954 (12.0 MiB) TX bytes:14766512 (14.0 MiB)
And this is the total traffic that has passed over the interface since it was created (most likely,