To place new components to the Web Application just drag the desired component from the upper panel and drop it to the place you want this component rendered. Every component has a popup with applicable settings. Usually, this popup can be opened by clicking the settings icon or component itself.
Some components like tables, views, forms need to have data sources. E.g. to fill a table with data, you need to specify an endpoint as the data source. Table columns will be automatically populated with selected endpoint variables and you can adjust them the way you want - from title to rendering options.