Disk I/O & Network I/O

HI Team,
I am working on ubuntu server through ssh, as its in US and i am in India. From last 4/5 days its working very slowly. It doen'st shows any load or more procsses, but works slowly. For that my senior told me to check Disk I/O & Network I/O of that server. Can anybody help me. I dont know how to check this, what command used for it and also how can we monitor it. What are the normal values of Disk I/O & Network I/O? Please help me out from this.

Thanks & Regards
Parag Nehete