I want to create an asset with aspects and write/read data to/from it.
The MindSphere API Document says that assets can be created using the API. Do you have a running code example for creating an asset via the API? Is it also possible to create it with the Web-GUI? If so, which account is necessary for that (type)?
At developer.mindsphere.io you will find the API documentation with examples. Specifically for an asset creation you'll need the Asset Management Service API. I recommend to play with APIs with an API testing tool of your choice, like for example Postman or Insomnia.
Sure, every MindSphere tenant has a web tool/app called "Asset Manager", which allows you to define Assets, Asset Types and Aspects usung the web GUI only.