For a start, when you collect cross- sectional data you are not concerned about the time period, Therefore, what you do is collect data from respondents across sections. For example, you want to check for difference in consumption pattern of any product across different regions in country considering one particular time frame. In conteast, you have time series data which you collect from a set of respondents across time period. For example, the consumption pattern of one particular resgion for the last ten years.
Longitudanal data actually incorporates this cross sectional data and time series data. In longitudanal data you can check for consumption pattern of a product across different regions for the last ten years.