The overall configuration really depends on whether or not you are using vLANs, multipathing, jumbo frames, trunking, number of uplinks on your ESX hosts, etc.
For a very simple config to get yourself up and running with the built-in Software iSCSI Adapter in ESX using a single Cisco swtich (can be any GbE switch, really), do the following. This is ideal for a lab or test environment.
Note: Anywhere that I use the term "SAN", substitute whatever you are using to provide or emulate iSCSI storage, be it Openfiler or another hardware implementation.
1) Connect one or two (for redundancy) uplinks on your ESX host to the switch using a CAT6 cable.
2) Connect the SAN iSCSI ports to the same switch and assign the iSCSI initiators on the SAN IP addresses.
3) Create a new vSwitch on your ESX host and configure it to use the uplink(s) you connected to the Cisco switch.
4) Create a new vmkernel network connection on that vSwitch and assign it an IP on the same subnet as the iSCSI SAN.
5) Connect to that ESX host using the vSphere client (or go through vCenter if you have it).
6) Click on the Configuration tab, select Storage Adapters.
7) Highlight the Software iSCSI Adapter and click Properties.
8) Click Advanced and check the box for Enabled and click Ok.
9) Go back into the properties of the Software iSCSI Adapter. On the Static Targets tab enter the IP addresses of the iSCSI targets on your SAN and enter any CHAP as necessary (if you configured it on the SAN, otherwise leave it blank). Click OK.
10) Back at the main Properties page, click CHAP and select the box to use the initiator name as the CHAP name. This sets the name of the incoming initiator so that you can use it to set up the initiator settings on the SAN.
11) Ensure that your SAN is set up to accept connections from the initiator names of your ESX hosts and that any CHAP settings match. Also make sure that the iSCSI LUNs on your SAN are configured to be presented to those incoming iSCSI initiators.
12) On the ESX host, Configuration tab, select Storage Adapters once again and click Rescan.
13) If all of that is set up correctly, you should see your iSCSI LUNs detected by the software initiator. Verify that the number of paths shown is correct.
If you are using the software iSCSI initiator and have two iSCSI targets to access the same SAN storage, you should see two paths per LUN. If the numbers don't add up, verify on your SAN that the ESX software initiator was able to log in to both iSCSI targets successfully.
14) Now, on the Configuration tab click Storage and Add Storage. You will now see the iSCSI LUNs available to create VMFS datastores.