How can I provide SSH key while creating a Linode?

You can add a pubkey to your Linode while creating a Linode. It's an option towards the bottom of the Create Linode page.

If you haven't added an SSH key for your Linode account yet, you will need to click the "Add an SSH Key" button. In the popup that comes up, give it a label, then paste the pubkey into the next key. Now, each time you create a Linode, you can select the check box next to that SSH key.