I have to try to create a new module in Magento but it doesn't work, I have to research on website and to do like they wrote but it still not working.
I do not have folder app/code I just have
app/design and app/etc,. So I must create in vendor/magento but I don't know how?
Can you help me, please
Welcome to community .
If you are facing difficulty creating modules in magento 2 , you can use https://mage2gen.com/ (here is your sample code) or any other module creator and compare them . This you can find out what were the files that you were missing or had error in them .
Hope you are creating
app/code/YourNamespace and placing your files there then running
bin/magento setup:upgrade before the first time that you are trying to execute you custom module.