How to make most of aws?
AWS has an excellent guide for deploying MongoDB on AWS.

https://d0.awsstatic.com/whitepapers/AWS_NoSQL_MongoDB.pdf

If you are looking for specific instructions on how do deploy MongoDB on AWS be sure to check this out:
https://docs.mongodb.org/ecosystem/platforms/amazon-ec2/

Also bear in mind that AWS micro instances are too small for any production use of MongoDB. If your goal is simply learn MongoDB and AWS the micro instances maybe fine, but for any performance/stress testing the results for a micro  instance would not be realistic.

Good luck!