Correct me if I'm wrong. At this moment, my router is in dynamic mode. Does this mean that it will get whatever the modem is sending? In that case, I should set the router to static IP. Then, I should set my PC to static IP as well; that way, it connects to the static IP of the router, thus, both being "synced".
Life is always changing ... we better get use to it!
Your router is probably in dynamic mode (DHCP). It is getting what ever IP address your ISP is sending. While your modem is in bridge mode, all it does is convert the signal from the format used over Coax (DOCSIS probably ... Data Over Cable Service Interface Specification ) to Ethernet. No IP address, no filtering, just translating. Generally then, yes, you will set the WAN port IP address to the static address they gave you, along with the other information (DNS, gateway, etc). Your computer will also get a static address, but it will be in the same subnet as the LAN port of your router ( router is 192.168.0.1, then computer could be 192.168.0.2). This address should be outside the routers LAN side DHCP servers address pool. It gets confusing becuase on the WAN side your router acts as a DHCP client (receiving) and on the LAN side it acts as a DHCP server (giving out).
Here is the thing ... each device should have a unique IP address. If you set your computer and the router to the static IP address your ISP gave you (which it kinda sounds like you were saying) then when a device on the internet calls up that IP address they both answer and things don't work (ok, not really, but kinda sorta). The key is that each device gets their own IP address for things to work right.
Once you have that setup, then you can open ports on your router to allow your computer to receive incoming IP requests. The thing that might confuse you is that your computer is at 192.168.0.5 (or whatever), but your buddy on the internet is typing in the static address your ISP gave you. When you forward (open) port 21, you tell the router that when it receives a message on port 21 (FTP), then it should forward that to 192.168.0.5. The whole reason we do this mess is that we can have multiple devices (computer, phone, printer, etc) all use the same public IP address because as you know the number of IP addresses available is limited. The alternative would be to get a static iP address for every device on your network (kinda expensive and not worth it).
Hope that makes sense.