Select the "Upload a file or drag and drop" option, and ensure that the CSV file is of supported size.
You have the ability to align the column from the imported file with the suitable contact field in the system. Additionally, there is an option to preview the aligned information in the preview column.
In case you have any column(s) that do not match, you must select the "Don't import data in unmatched column" option to proceed to the following step. Unless you check this option, you cannot proceed to the next step.