Cat-proofing balcony

Hey guys. Is there anyone here, successfully catproofed their balcony on their own? I am a new kitten parent. Till now, I was able to strictly keep them indoors and didn't allow them to the balcony since they were new to the place. Now they got comfortable and started exploring all places of the house. I thought of keeping the balcony doors closed all the time but it's not feasible long term. Do you any of you catify your balcony on your own. If so please help me with ideas and links of thing you bought online. Also for windows. Any ideas and suggestions are appreciated. Thanks in advance.