added some examples

20250227/demo_app/App.tsx

@@ -1,10 +1,19 @@
 import { StatusBar } from 'expo-status-bar';
-import { StyleSheet, Text, View } from 'react-native';
+import { Button, StyleSheet, Text, View } from 'react-native';
+import { useState } from 'react';
 
 export default function App() {
+  let [counter, setCounter] = useState(0);
+
+  let increment = () => {
+    setCounter(counter + 1);
+  }
+
   return (
     <View style={styles.container}>
       <Text>Ez az első mobil appunk!</Text>
+      <Text>A gomb ennyiszer lett megnyomva: {counter}</Text>
+      <Button title='nyomj meg' onPress={increment}></Button>
       <StatusBar style="auto" />
     </View>
   );