snmp configuration

hello guys.
i recently start using zenoss core enterprise v4.2.0. i have some question and i hope can find the answers here.

1- i added a linux sever in to zenoss.
first i added the server from:
add multiple devises --> Linux Server (SSH)
then i added the device from:
add a single device --> /Server/SSH/Linux

but the view was different. at the first time i had component in the main window. but at the second time i didn't have a component view.
now i wonder why this happened how can i mange the component view

2- i installed the snmp v2 in the client server. but in networks view snmp status is down.
here is a photo which i took:
http://s28.postimg.org/80hkxlndp/image.png
http://s27.postimg.org/t1eu0ajlv/image.png

3- how can i monitor the network card throughput in a graph

4- what is your recommendation for monitoring the linux servers(specially oracle products like: oracle database, oracle application and ...)

5- is there a tutorial for beginners like me
thank you.