@rashi1101 I hope
@yyzstudent did not mean to offend you. He/She might be suggesting to start with the online form as it is self explanatory.
Now as you indicated, you looked into online application guide, Not sure which one, link would help.
But during the course of my application submission which I submitted on Dec 2022, I was required to upload following:
1. digital citizenship photo
2. Two personal identification document like passport and DL.
3. again uploaded passport and visas under "Travel documents or passports"
4. Language proof.
The application has physical presence calculator inbuilt. And let's say if you fill your application today and choose to submit at later day, the application will force you to revisit physical presence section just to confirm there is no change since last update.
Regarding the "Other supporting documents" which is optional, I did not submit anything because my application did not have any complexities that I had to explain or support by providing evidence. So if you have any, use this section.
Currently, I am done with my BG check and citizenship exam. So I guess I did so far good without uploading any additional documents.