In different views - like card vieow , list view , column view etc , you would see the thumbnail , and also in side rail when dragging/dropping assets on pages and many more places you will see use of OOTB renditions.
You can generate custom renditions / check these renditions in DAM update workflow.
Sorry, maybe there is something wrong with my statement, what I want to ask is how do I use it in the component. Now I can only see the original assets stored in the dam in the component and can't use the renditions,I want to use the renditions.
This cannot be done through drag/drop directly on the component but in your component logic you can refer to the path of the image rendition e.g. You could add a dropdown with all possible rendition options and based on what is selected in dialog image url is rendered as
<img src="<dampathofimage>/jcr:content/original">
or<img src="<dampathofimage>jcr:content/<rendition1>" Example :-