Azure SQL is not an HTTP/s service-- it runs proprietary SQL Server protocol on port 1433, just like on-premise versions of SQL Server.
If you are trying to connect directly to SQL Server from a Xamarin App, you are almost certainly making a mistake. Doing so would require providing credentials to your Xamarin app that can connect directly to your database, which opens your database up for a malicious user to do pretty much whatever they want to. The reason this kind of 2-tier application is dangerous is because the Xamarin app runs on an untrusted device (your user's mobile device), and a malicious user can intercept any data that your application has in memory, including your database credentials. They can then use those credentials to gain access to your database. Unless you were to use unique database credentials for each user (very impractical) and setup very stringent security roles in SQL Server, it'd be impossible to keep a malicious user from accessing the database for all of your other users (which is very, very bad). The other problem is that many networks block traffic on port 1433, or only allow access via an HTTPS proxy server, so your application would not function on many networks if it tried to connect directly to SQL.
This is the answer to your question, but please don't do this:
If you are certain that you have taken care of the security correctly, you should be able to install the System.Data.SqlClient nuget package and use that to communicate with SQL Server as you would with any .NET application. Here's a code example from Microsoft.
This is my opinion on what you should do instead:
The correct way for most Xamarin applications to communicate with Azure SQL database would be via an intermediary application server.
If your application access data specific to a user, should have per-user credentials in it (username and password that get exchanged for an authorization token when the user logs in is a common technique). The Xamarin app would then use HTTPS to make requests to your application server using those user credentials. The application server would validate the user credentials (authenticate that they are legitimate and authorize the data being requested based on who the user is) and make requests to Azure SQL.
If your application only access public data anonymously, then you can make unauthenticated requests to your application server which will blindly request that data from Azure SQL and return it to your client (though it would also return the same data to any attacker on the internet, so be sure if you use this approach you intend all data served to be public to the world).
In both cases, your application server would be the only piece that communicates with Azure SQL. For a .NET application this would typically be done via System.Data.SqlClient or perhaps indirectly through an ORM like Entity Framreworks. The advantage to this 3-tier approach is that the untrusted client tier does not have unrestricted access to your database tier. Only the middle application server tier has the credentials for SQL Server, and it is trusted and runs in a secure environment (a server you manage, not an end-user's mobile device). This means that an attacker cannot intercept the database credentials and misuse them. It also means that your application only requires HTTPS data access to function, so your application will work on almost any network.
This is probably not the answer you are looking for, since it involves authoring an entire application server that has to be hosted by you (Azure App Service would be my recommendation, if you are already using Azure SQL). It also requires you to implement an API on the server, and then write an API client for your Xamarin application. This is no small amount of work.
