How to block a contact in Gmail?

1. Click Contacts from the left side of Gmail.
2. Select the person you'd like to block.
3. Select Block from "Show in chat list" Box.

To unblock 
Just select Always or Auto from the "Show in chat list" Box.
OR
Type their name in the Search, add, or invite field at the top of your Chat list. Then, in the blue box that appears, hover over your contact's name and select Show in chat list.

Can I insert 'Photos' in Gmail? (Without using attachment link)

It's a new facility in GMail.

• Login GMail
  
• Click settings->Labs
• Scroll down to inserting images
• Click enable

From now on when you compose a mail in GMail, you will get this 'Insert Image' option.

How do I forward my Gmail to another email account automatically?

• Log in to your GMail account.
• Click Settings (at the top)
• Click Forwarding and POP/IMAP (at the top of the Settings box)
• Enter the email address to which you'd like your Gmails forwarded.
• Click the drop-down menu (in the next line)
  Choose "keep Google Mail's copy in the inbox" or
  Choose "Archive GMail's copy" or
  Choose "Delete GMail's copy"
• Click Save Changes.
  

You also can set up filters to forward selected GMails
You can create upto 20 filters