I realise you might be new and so I am trying hard not to be rude, sarcastic or sound like one of those elitists. I am not going to be mad. I am not going to be mad. I am not going to be mad. Phew!
Now that I am calm, and before I answer your question, which is not stupid at all, let me teach you a life lesson. It is always important to search whatever forum you are posting to and see if someone has not gone through a similar problem in the past. If so, copy the solution and implement it.
The question you have just asked has been asked countless times before and simple search should have yielded the answer. I am a polite person so i am not going to tell to go RTFM! Instead I am going to do the mature thing and answer the question:
Your phone is old, its firmware is so old the Certificates (or more correctly CAs) are old and have expired. The phone has reached its end of life cycle and is no longer supported. You cannot download certificates because the shop is closed its over. That's why you got the phone on the cheap side. It's time to upgrade buddy because there is no fix, there will never be a fix. You cannot install Whatsapp or any app that requires encrypted connections on it. You are going to have problems accessing https://google.com
The long and short of it is you are screwed buy a new (android?) phone. Do not buy a Blackberry phone because if you do you are going to run into problems and come back running to this forum and I cannot promise that I will not shout at you.