Basically, the journal wants to know whether you wish to continue with them and are ready to make the suggested changes. This is because some authors might not want to make changes that require a lot of time and effort and would rather submit the paper to another journal. If you are willing to make the changes, you should click on the "Agree to revise" button now. That way, you just inform the journal that you intend to continue with them. You will not be expected to make the revisions and submit the revised paper immediately. Once you agree to revise, you will probably be assigned a deadline for submitting the revised manuscript. If you feel that you will not be able to submit within the deadline, you can write to the editor requesting an extension and mentioning a preferred date of submission. However, once you're granted an extension, make sure you do not breach that deadline.
- Can I extend the journal submission deadline for my revised paper?
- Could the paper be rejected if the due date for submitting revisions is over?