Will I lose all my photos?

I am having storage problems on my PC. I moved what I thought was everything to an external hard drive only to find out that icloud is taking up 424GB of storage on my computer. I would like to move it all to my external hard drive but I am worried about losing all of my photos in icloud. Shouldn't icloud have it all.....in the cloud?? Why is it all stored on my laptop? I would like to be able to free up space so my laptop can work again!