It depends on which Cisco Router you have but here are a common list of interfaces that can be found, or if modular, can be added to a router.
serial interface commonly used for WAN connectivity configured as either frame relay or PPP (Point-to-point). Speeds from 64kbs to 512kbps. Usually connected to a modem.
Ethernet/Fast Ethernet/Gigabit Ethernets commonly used for LAN connectivity but nowadays can also be used for WAN or MAN. Also known as the IEEE 802.3 specification.
E1/T1 (controller e1/t1) interfaces are either channelized or unchannelized interfaces with speeds up to 2.048Mbps. Channelized T1/E1 interfaces can be enabled to create serial interfaces from 64kbps (DS0) to either 2.048Mbps T1 or 1.544Mbps. These sub-channels can be grouped to create a higher bandwidth channel.
POS (Packet over Sonet) interfaces. I don't have much idea on these types of interfaces but they are commonly used for WAN using the SONET/SDH infrastructure as trasmission facility. Speeds from T3(45Mbps) to STM-16 (2.8Gbps)
ATM (Asynchronous Transfer Mode) interfaces. Also commonly used for WAN connectivity utilizing the ATM network infrastructure as transmission facility.
Old technology interfaces such as ISDN-BRI and Token Ring were also used before.
Other interfaces used for different services such as the FXS and FXO for IP telephony are also commonly used. I'm not very much familiar with these so I guess you have to do some research about them if you are to use them.
Different types of routers uses different types of modules which are specifically coded to identify which series of routers they belong such as the port adapters (PA-XX) or the network modules (NM-).
Most high-end routers have hot-pluggable modules. These can be accessed via the ever reliable command line interface (CLI). Good thing about Cisco is that these routers are easy to manage.
The Cisco.com site has all the resources that you need and often provides sample configurations that are very helpful in implementing different network setups.
We are pleased to announce availability of Beta software for 16.6.3. 16.6.3 will be the second rebuild on the 16.6 release train targeted towards Catalyst 9500/9400/9300/3850/3650 switching platforms. We are looking for early feedback from custome...