Update 'How to Use the Capture Checker'

Author: bracevac

docs/_docs/reference/experimental/capture-checking/how-to-use.md

@@ -6,7 +6,48 @@ nightlyOf: https://docs.scala-lang.org/scala3/reference/experimental/capture-che
 
 ## Enabling Capture Checking
 
-TODO
+Use Scala 3 nightly for the latest features and fixes.
+
+Add this import in any file that uses capture checking:
+```scala
+import language.experimental.captureChecking
+```
+
+### Separation Checking
+
+Requires the import above:
+```scala
+import language.experimental.captureChecking
+import language.experimental.separationChecking
+```
+
+### SBT Project Template
+
+Alternatively, you can clone a pre-defined SBT project to get
+started: https://github.com/lampepfl/scala3-cc-template
+
+### The REPL/Scala-CLI
+
+Using the command line through explicit parameters:
+```bash
+scala -S 3.nightly -language:experimental.captureChecking
+```
+or when reading from a file:
+```scala
+// foo.scala:
+//> using scala 3.nightly
+import language.experimental.captureChecking
+...
+```
+Then, it suffices to run
+```bash
+scala foo.scala
+```
+
+## API Documentation
+
+Scaladoc supports capture checking. The nightly standard library API docs have it enabled by default:
+https://nightly.scala-lang.org/api/
 
 ## Compilation Options