I have purchased the SSL certificates and need to obtain CSR. Is it mandatory to have CSR for SSL? I am using Bluehost hosting services.
If you have access to your web server you can generate your own CSR, otherwise, your hosting provider or server administrator will need to help you. Some well-known control panels (Ensim, Plesk, cPanel, etc.) will allow you to generate your own CSR if your hosting provider has enabled that feature for you. How you generate your CSR depends on the brand of web server software your domain is hosted on. In your case, Bluehost has given step-wise guide to obtain a CSR, here.
Also, its important to have CSR for SSL. You must have a CSR for your domain before you can apply for an SSL certificate.