Welcome to Workshop @ratnanannapanen. It's fantastic to have you join us and we hope you find lots of helpful information and inspiration for your projects from our clever and creative members.
Can you please tell us what type of door you need to install? Is it a traditional hinged door or perhaps a cavity sliding door? Even a photo to show what you are working with might be handy for members to give you a comprehensive response.
One resource you might consider using if you don't want to do-it-yourself is hipages, where you can get a quote from local tradespeople.
I'm sure from the videos you will find that it's a very achievable D.I.Y. job, and you can certainly ask our experienced community members here on Workshop if you have any questions or get stuck at any stage in the job. We have loads of members who are happy to share their knowledge and experience.