Anu - what exactly do you mean here? Do you mean available online in academic social sources - such as RG - or online within the journal that it is already published with? If the journal - it depends if it offers that facility or not.
Very simple, just scan the paper or chapter that bears your contribution from the volume and upload to the relevant platforms you desire such as Researchgate, Academia.edu and others.
Several tools online can help you to join the pages of your work into a complete document.
@Anu you can just Google "PDF conversion" or "word to PDF" online and you will find several tools that you can use for that purpose. Some, you have to pay for them while others may offer you free but limited subscriptions or membership opportunity. I hope this helps!