1.i just learnt about Tor, and i'd like to know where is the best place to download Tor browser,i feel downloading from the google play store or another browser might have a negative effect on the purpose i'm using it for. 2. do i have to use VPN with TOR? 3. how safe am i using TOR browser?
For the first question: It depends on which OS you are using. If you are using any Linux distribution or BSD. You are better off getting tor via the built-in package manager. They will automatically download, verify and install tor for you. If you are using Windows (I'm not sure about OS X). Getting Tor using another browser is going to be your best option. And if you are technical enough, remember to verify your download using Tor's GPG signature. Verifying detects and stops you from executing malicious code in case someone have tempted with your download.
For the second question, it depends: Unless you live in one of the continues that sensors the Internet or are using Tor under a heavy firewall. You don't.
For the third question, again it depends. Tor is a anonymizing network, and it provides security by giving you privacy Assume for a second that you are a journalist in a war zone. You get killed if the military knows who you are. So you use Tor to avoid that. It hides your IP and identity. It prevents governments and cooperation from knowing who you are given you are using Tor correctly. - That is, don't do stuff that defeats the entire point of Tor. Like, cooperation can still track you if you logged into your account with a real identity connected to it. And, Tor won't block malware nor it prevents phishing. Tor is a powerful tool. But it is not a magic pill for all security problems.
It is perfectly safe to download TOR through your browser.
DO NOT use a VPN with TOR. Adding more hops is discouraged by the Tor Project. Using a VPN with TOR can open you up to more potential security opportunities for your traffic to be tied to you.
For the average person, very safe, much safer than browsing in the clear. There are known vulnerabilities in the TOR Network, though for the most part, only have the potential to be abused by large APT's or Nation State's that have millions in resources.
If you want to just browse sites without being tracked, you're fine using TOR.
Some users go as far as installing a dedicated amnesiac operating system called TAILS that leaves no traces on the computer it is run on. But for most use cases would be a bit extra.