To read data on your analytics first you need to retrieve data from your digital platforms to GA4 in the form of the data stream. A Data Stream is actually the Data source coming up from multiple platforms.
In the GA4 account, there can be a number of data streams because data is coming up from multiple resources like a website, an android app, and an IOS app.
It totally depends on a user of GA4 to create the numbers of data streams in accordance with their digital assets.
You can also watch the video for more details about the whole procedure.
Here is how you can set a Data Stream:
Step 1: Navigate to the admin section
Step 2: Go to the Property
Step 3: Go to the Data Stream
Step 4: Click on the Web button (if you want to set up for website)
Step 5: Fill up the details
Step 6: Click on the Create Stream button
The data stream will be created showing all the aspects of your data resource.