Update "Build a subset of the code" section (#27976)

* Update "Build a subset of the code" section

* Address feedback from peer review

Author: captainsafia

docs/BuildFromSource.md

@@ -278,9 +278,21 @@ On macOS/Linux:
 
 ### Building a subset of the code
 
-This repository is large. Look for `build.cmd`/`.sh` scripts in subfolders. These scripts can be used to invoke build and test on a smaller set of projects.
+When working in the repository, you'll typically be focused on one project area, such as Blazor and SignalR. In that case, it's easier to use the `build.cmd` and `build.sh` that are available in each subfolder. When invoked in a subfolder on Windows:
 
-Furthermore, you can use flags on `build.cmd`/`.sh` to build subsets based on language type, like C++, TypeScript, or C#. Run `build.sh --help` or `build.cmd -help` for details.
+```ps1
+.\build.cmd
+```
+
+Or on macOS or Linux:
+
+```bash
+./build.sh
+```
+
+> :bulb: Before using the `build.cmd` or `build.sh` at the top-level or in a subfolder, you will need to make sure that [the dependencies documented above](#step-2-install-pre-requisites) have been installed.
+
+These scripts will build and test the projects within a specific directory. Furthermore, you can use flags on `build.cmd`/`.sh` to build subsets based on language type, like C++, TypeScript, or C#. Run `build.sh --help` or `build.cmd -help` for details.
 
 ### Build properties