Let's say that you have Finance department in your company and you want to track the cost of serverless compute generated by that particular department. First you need to create budget policy. To create budget policy, go to your databricks workspace and click settings (1):

Now, in Setting page click on compute (2) and then under Policies click manage (3) to configure Serverless budget policy:

Now, click create button (4):

Now, provide a name for your budget policy and all tags that should be part of that specific policy and click create:

Once you created serverless budget policy you can associate it with job/notebook/pipeline or serving endpoint which will allow you to track the cost. 
For instance, I've created a notebook that I'd like to run with serverless compute and track cost. Connect to serverless compute and then go to configuration:

Now, selected policy you want to apply (in my case Finance Department policy):

After a policy is applied to a notebook, job, or Lakeflow Declarative Pipelines, any tags contained in the policy propagate to your system.billing.usage system table in the custom_tags column.