Hello everyone
I have 2 questions
but nothing is getting updated and also i am not able to figure out the modal popup location
any help would be appreciated
What do you want to change, exactly?
Most modification can be easily implemented as a CSS customization, which doesn’t require mucking with Discourse internals 
i want to change some html tags and placement of login and some other pages
That may be possible with CSS, depending on what exactly you want to do.
If you draw a mockup of what you want to have (an ugly Paint drawing based on a screenshot is fine!), one of the CSS wizards hanging around here will probably be able to help you out
ok i want to change html elements for example in category page i want to add a floating button .
in login and signup page i need to add a logo and another image and want to also edit login function, (i want to add a rest api request to my server with login prompt)
Some of these changes may require adding elements to plugin outlets – here is the easiest way to do that:
How do you want to change login functionality, exactly?
This sounds like you might be interested in SSO:
ok thankyou but i want to keep a track of users in discourse also for som reason thats why i needed to add rest api,
and for category also i want to add a image and change placement like i want to add a floating button
Again, this sounds like you want to use CSS customizations and plugin outlets. Without a more detailed description or mockup of what you want to do, I’m afraid I cannot provide any additional help.
While this is quite vague, it sounds like what you want to build would be insecure. Depending on what exactly you want to accomplish, SSO, the Data Explorer or a custom plugin might help you, but we need a detailed description of what you want to have to help you.
for category i want to add a small image before each category name for ex
for login i want to be validated the user from my server before login to discourse server
ex: if user enters email and password i want to send it to server if user existing in my server then continue discourse logins otherwise display message as user not existing
is this details give an idea what i want to do
i have also attached a small diagram what i want
If I’m understanding correctly, having an image for a category is already possible via the category create / edit modal.
The automatic switch is a good idea, but I don’t know how code would determine between an existing account that was a typo fail and a new non existing account.
This absolutely sounds like you want to implement SSO 
If i want to use a rest api request from another server how can i do that with discourse,
for example lets say if i want to add some articles from a different server which is using rest api and json to the category page in discourse
