Since you are "extremely new" to networking, let me give you some pointers on the OSI model:
- It's just a model -- that is, a mental construct
- It was developed by a committee
- No protocols (in use) actually follow it
Many new networking students spend an inordinate amount of time trying to figure out "which layer" a protocol or function belongs to. It is a fool's errand, because whatever protocol you are looking at was not designed with the OSI model in mind. So you are forcing it to fit into an arbitrary model. That's fine, I suppose for entertainment's sake, but it won't really help you understand networking any better.
Many protocols straddle different layers of the OSI (and TCP/IP) model. Is ICMP layer 3 or layer 4? Is ARP layer 2 or layer 3? Perhaps a little of each. MPLS? Don't get me started.
The important thing about all models (here's one that things actually follow sometimes http://www.sis.pitt.edu/~icucart/networking_basics/4LayersofTCPIPModel.html ) is that there ARE layers. And layers have interfaces to the ones above and below it. So you can replace the functions of a layer with another, and as long as the interface between the other layers stays the same, everything works. So, for example, you can replace one layer 3 protocol, IP version 4, with IP version 6, and everything else will continue to work exactly as before, because IPv6 communicates with layer 2 (below) and layer 4 above) in exactly the same way as IPv4.
The other thing to remember about layers is that, for the sender, a layer encapsulates the data (technically, the protocol data unit, PDU) of the layer above it. So layer 3 encapsulates the layer 4 data unit, layer 2 encapsulates the layer 3 unit, etc. The receiver reverses the process, decapsulating the data and handing it off to the layer above it.
Sander's post about ARP, BTW is right on.