I am quite new to this, and started using Electrum today. I read on the Bitcoin Wiki that "unlike e-mail addresses, people have many different Bitcoin addresses and a unique address should be used for each transaction". Under the "Receive" tab in Electrum, I found a long address. Is that "Receiving address" the one that should be unique for each transaction? If that's the case, does Electrum generate a new one for me after receiving or do I have to do something myself?
Generally you do not need to manage your addresses yourself. Your wallet software will handle that for you and generate new addresses for you when you want to receive Bitcoin. In Electrum, just use the receive tab and get addresses from there. As you use addresses, you should see that the address in the "receiving address" box should change.