Hi @amirabedhiafi ,
1) In order to display anything on the report, you need data. So once you import data from Excel or database to your Power BI desktop file, you created a dataset for that report.
2) One Report has one dataset, but this dataset can include multiple data sources. Example, you can import data from one csv file, from one Excel file, from sql database. All these different data sources are actually one dataset used for this report.
3) Once you publish your report to Power BI Service, you will see that you actually uploaded 2 things: report and dataset. So as mentioned in previous step, your report has one dataset.
4) But now once this dataset is published, other reports can also use this dataset. You can see that option in Power BI desktop application when you go to Get data > Power BI datasets
5) Dashboard is used on Power BI Service and it is actually combination of different reports. You can take one chart from one report, second chart from another report and combine it in 1 dashboard. Dashboard itself doesn't connect to dataset, it connects (by clicking on dashboard chart) to report that is source for that chart.
Hope this helps.
Regards,
Nemanja Andic
