Before applying for IISER admissions , you must have a scanned copy of your 12th class marksheet in PDF ,JPG or JPEG format .The maximum size of this is one MB.After entering your marks , you will see a Click here to upload button .Click on that button .A popup will appear with a Browse button .Click on Browse button and then browse the soft copy of your 12th class marksheet to upload.Browse it and upload it .Upon successful uploading , you will see the filename along with file uploaded successfully. And this is how your 12th grade marksheet gets uploaded.Hope you understood it 

Feel free to ask any further queries!

Hiiii dear!!!! To upload the marksheet of your 12th boards, you will have to click on the option of upload of 12th marksheet which you will come across while filling the section of academic part. There you will require to scan the marksheet and then upload it.