The sequence of the numbers that is the OID are the identifiers of the branches of the tree. Every subtree in the tree is assigned by the IETF to ensure that all branches are unique. Each branch has a name and a number assigned to it. All SNMP objects are somewhere under the subtree iso.org.dod.internet which is 1.3.6.1. The MibII definition can be obtained from RFC1213 .
Scalar values are easy to read.
Reading elements of a table is a little bit trickier then reading simple values. Each of the question marks stands for one number of the ip. Of course to read this value you would need to know it exists. IpAddress is element of table indexed by this address itself. SNMP solves this problem by supporting a command set that allows the user to search its data tree.