First, I usually have my data like this. Notice that I am using Excel and I save my data as CSV comma delimited.
You have to use the "Data Source Manager", either by the icon in the GUI or Layer/Data Source Manager. You have to choose the "delimited text" option. This is what you will see:
Then you have to fill the appripiate fields like:
Geometry Definition. In this one it is mandatory to select the proper Coordinate reference system at "Geometry CRS". My data is lat lon WGS84, so I use EPSG 4326. If your data comes in a projected CRS you must choose the proper EPSG code.
You will see an example of the way Qgis is understanding your data. This is an example:
Now choose the button add, and thats it. This is the resulting map with the data in the second image: