To request bitcoin from someone else they need your "receiving address". You get your receiving address by choosing the "Request" tab or selecting the "Trade | Request Bitcoin" menu option.
At this point MultiBit Classic will be able to show a QR code that a Bitcoin wallet on a mobile phone could use to send you bitcoin. The QR code contains the address, the label and the amount all in a convenient format.
Bitcoin makes it easy to share your receiving address over the Internet. For example, copy your receiving address to the system clipboard by pressing the "Copy" button. Then paste the address directly into an email, Skype chat session etc to give it to the person sending you bitcoin.
You can also copy the generated QR code by pressing the "Copy" button in the right hand side panel. You can then send the QR code as an image to the payer by email, Skype etc. To help you with this if you drag the QR code directly to your desktop MultiBit Classic will turn it into a PNG image file automatically.
You can have as many receiving addresses as you like. MultiBit recommends using a different receiving address for each person that is sending you bitcoin so that you can tell them apart. You create new receiving addresses by clicking on the "New" button on the "Request" tab.
In the "Label" field you should add a label to the receiving address to help you remember who is sending you bitcoin.