Why it matters
AWS's scale means that its choices become industry defaults. IAM patterns, VPC networking models, and S3 storage semantics have been copied by every other cloud. Learning AWS is learning the base vocabulary of cloud computing.
Cost management on AWS is also existential for many businesses. The same service that costs $100 a month when configured well can cost $10,000 when configured badly.
The architecture
AWS is organized into regions (independent geographic areas) and availability zones (isolated datacenters within a region). Each region has 3+ AZs to enable HA architectures. Cross-region traffic is metered; cross-AZ within a region is much cheaper.
Services layer on top: compute (EC2, ECS, Lambda), storage (S3, EBS, EFS), networking (VPC, ELB, CloudFront), databases (RDS, DynamoDB, Aurora), and hundreds more.
How it works end to end
IAM (Identity and Access Management) governs who can do what across every service. Every request is authenticated (via keys, roles, or federated identity) and authorized against IAM policies.
VPC (Virtual Private Cloud) is the network primitive. Every EC2 instance, Lambda, and RDS lives in a VPC. Subnets partition VPCs by AZ and by public/private.
Services communicate over the AWS backbone with private endpoints; public internet access requires explicit configuration.