Azure services have different charging models.
It's important to understand what services you have deployed, if their costs are static or if they fluctuate based on usage.
Generally speaking, yes - deleting resources will lower your Azure spend. However some Azure resources are free, and some have a free tier.
Azure Cost Management provides views into your spending, which you can use to investigate which services/resource-groups are costing your the most; https://learn.microsoft.com/en-us/azure/cost-management-billing/costs/quick-acm-cost-analysis#analyze-costs-with-smart-views