The problem
AWS is great. IAM Policies are nightmare.
Here is a simple policy generator for giving full access to a single bucket in AWS.
S3 Bucket Details
Enter your unique bucket name
IAM Policy
...Summary
Security is hard, but you can use this as a starting point for writing your own policies.
Always review IAM policies yourself before implementing them and make sure they fit your needs.
For example, do you need write access? Do you need access to all the directories in the bucket? You can restrict access further to make sure your AWS account stays secure.