diff --git a/4. Core Module/app.js b/4. Core Module/app.js
new file mode 100644
index 0000000..8f1c145
--- /dev/null
+++ b/4. Core Module/app.js	
@@ -0,0 +1,31 @@
+// Core module
+// File system
+const fs = require("node:fs");
+
+// Write string to file synchronous
+// try {
+//   fs.writeFileSync("data/testSynchronous.txt", "Hello World Synchronous");
+// } catch (error) {
+//   console.log(error.message);
+// }
+
+// Write string to file asynchronous
+// fs.writeFile(
+//   "data/testAsynchronous.txt",
+//   "Hello World from asynchronous",
+//   (e) => {
+//     console.log(e);
+//   }
+// );
+
+// Read the content of the file Synchronous
+// const data = fs.readFileSync("data/testSynchronous.txt", "utf-8");
+
+// console.log(data);
+
+// Read the content of the file Asynchronous
+fs.readFile("data/testAsynchronous.txt", "utf-8", (err, data) => {
+  if (err) throw err;
+
+  console.log(data);
+});
diff --git a/4. Core Module/data/testAsynchronous.txt b/4. Core Module/data/testAsynchronous.txt
new file mode 100644
index 0000000..6f47af8
--- /dev/null
+++ b/4. Core Module/data/testAsynchronous.txt	
@@ -0,0 +1 @@
+Hello World from asynchronous
\ No newline at end of file
diff --git a/4. Core Module/data/testSynchronous.txt b/4. Core Module/data/testSynchronous.txt
new file mode 100644
index 0000000..520ead9
--- /dev/null
+++ b/4. Core Module/data/testSynchronous.txt	
@@ -0,0 +1 @@
+Hello World Synchronous
\ No newline at end of file