How to downlaod images from planet? Are they free of cost? Which is the best way/platform to process this planet imagery data?

Dear All,

I am newbie to this platform (Planet imagery). I want to know how to download the images? and didn't see anywhere download option, if it's downloadable, will it be free of cost? If I am able to download then, which is the best platform to know how to process these planet images? Can we process this image as other optical images like Landsat, Sentinel 2 & 3. What else is the best place to clear queries on planet images.