Power BI is (mostly) the combination of two Excel plugins, Power Query (Get data from Excel 2016 onwards) and Power Pivot. The visual/report layer is an advanced version of Power View in Excel.
You have two options. First you can use Excel to have the Power BI experience in getting and connecting the data together. For this method you will use the Power Query (M) and Power Pivot (DAX) parts, these are the same as getting data and using the relationship designer in Power BI. If you are currently copying and pasting visuals from Power BI into Excel, then this method would be the best way. You may want to create your visuals in Excel, and format them to a Power BI look and feel.
The second option is to create the dataset in Power BI, getting and transforming the data, then publishing it to the service. You can then use 'Analyze in Excel' to connect Excel to the dataset and surface the data in Excel.
I would recommend not copy and pasting visuals from Power BI to Excel as you lose the benefits of Power BI's interactivity, just use the normal charts, slicers and other tools in Excel. By using the first option, you are keeping the workflow in one application without any convoluted steps back and forth, and anything you learn and use in Power Query and Power Pivot you can use in Power BI.