Basic Tier:

• The Basic Tier is the entry-level offering of Azure Service Bus.
• It only supports the queues, basic tier does not support topics, and subscriptions.
• The Basic tier is designed for simple messaging needs and is suitable for small workloads or testing scenarios.
• it has a pay-as-you-go pricing model, with a lower cost than the standard and premium tiers.
• It has lower throughput and message size limits than the standard and premium tiers.
• It does not support features such as auto-forwarding and scheduled messaging.
• It does not have the same level of security, compliance, and governance features as the standard and premium tiers.
• It doesn't have a built-in VNet support.

Standard Tier:

• The Standard tier is an enhanced version of Azure Service Bus that provides additional features and capabilities than the Basic tier.
• It provides a set of core messaging capabilities, including queues, topics, and subscriptions.
• The Standard tier is designed for basic messaging needs and is suitable for small to medium-sized workloads.
• It provides a shared infrastructure, which means that resources are shared with other tenants.
• It has a pay-as-you-go pricing model and provides a set of predefined throughput units.
• It provides features such as auto-forwarding and scheduled messaging.
• It has better security and compliance features than the Basic Tier.
• It supports features such as partitioning, which allows for higher throughput and message size limits than the Basic Tier.
• It doesn't have a built-in VNet support.

Premium Tier:

• The Premium tier is a more advanced version of Azure Service Bus with more features and capabilities than the Standard tier.
• It provides a set of core messaging capabilities, including queues, topics, and subscriptions.
• The Premium tier is designed for enterprise-grade messaging needs and is suitable for large-scale workloads.
• It provides a dedicated infrastructure, which means that resources are dedicated to a specific tenant.
• It has a consumption-based pricing model and provides a set of predefined throughput units.
• It provides features such as auto-forwarding, scheduled messaging, and partitioning.
• It has better security, compliance, and governance features than the Standard Tier.
• It has built in support for VNET and private endpoint 
• It provides enhanced performance features such as active-active replication, which allows for automatic failover and disaster recovery.

Summary

I hope the above explanation helps you understand that the Basic tier is the entry-level offering of Azure Service Bus. It's designed for simple messaging needs and is suitable for small workloads. The Standard tier provides additional features and capabilities over the Basic tier, making it suitable for small to medium-sized workloads, while the Premium tier provides the most advanced features and capabilities, making it suitable for large-scale workloads and enterprise-grade messaging needs.