With no other information we aren't going to be much help here. You cannot just throw stuff into Azure and it works. You need to have some basic level of understanding of Azure resources, your business requirements and how to configure everything. You can either learn all this yourself or you can hire a consultant to help get the initial stuff set up.
At a bare minimum you'll need a subscription in Azure. Then you'll need a resource group to hold the resource(s) you need. You can probably start with a single RG for your entire application but you may need to expand out later.
For your web app, for the cheapest cost, you'll need an Azure App Service to host it. This is where your web app will run. It'll be associated with the RG you created. This is literally just the web app so you can select the OS/configuration that is minimal for what you need to host. Most web apps are very lightweight so it shouldn't require much resources at all.
For your DB ideally you will use Azure SQL Database or perhaps Azure SQL Managed Instance. In either case the DB will be hosted directly in Azure, not in your app. This is where the cost is going to come into play. You need to configure the resource for your expected needs which you may need to adjust over time. For example if your DB is small then you don't need much storage. If your app is for a few people then you don't need a huge amount of processing power either. You can scale later.
Next you need to address security because you don't want people accessing your DB directly. Your app will need access (along with perhaps your local network) so you'll need to configure network security. This is really where things start getting hard. You'll want your web app to have access but no other public access.
To deploy your app you can either copy it manually or ideally use Visual Studio Publishing directly in VS. You'll point it to your Azure app service. You may need to adjust your Azure security to allow this to work. If you're using CI/CD process then they all support publishing to Azure as well. For the DB you'll need to do something similar.
During publishing you should configure your app to point to the Azure SQL Database you configured already (the steps are in the links given earlier). If for some reason you didn't do that then you'll need to edit your Azure App Service and change the settings manually in the UI via the Azure Portal.
This is a lot of work. Again, if you have no Azure experience this may be too much to do on your own. You probably need to get someone who can help walk you through the process at least the first time. If you don't then you're going to be wasting a lot of time getting this right.