Idea Validation

Hello! I am going to make a link shortner(my first project). Can you please elaborate me on it?
How to make audience before launching my product??
How can I conduct market research(there is very less information on this market)?
information about free/paid(not very costly since I am just a student LOL) marketing tools?
I don't want to scale it much but how to reach 500$(considerable amount in india)?
And also any insight for this newbie hacker will be really helpful, Thank you in advance!