i am using high sierra on MacBook pro 2011...how can I keep it safe and secure..?

izumacuser wrote:

how can I keep it safe

The fact that you mac is 13 yrs old and the macOS 10.13.6 last update was November 12, 2020.... is the best you can do.

Third party browsers may keep updates rolling out for your older system.

You can review —

Set up your Mac to be secure

Set up your Mac to be secure - Apple Support

Protect your Mac from malware - Apple Support

Protect your Mac from malware - Apple Support

Effective defenses against malware and other threats

Effective defenses against malware and ot… - Apple Community

Recognize and avoid phishing messages, phony support calls, and other scams

Recognize and avoid phishing messages, phony ...

It never pays to get too far behind in the hardware or software if "keep it safe" is a high priority concern.

In addition to updating third party browsers, security is primarily maintained through the use of passwords. That means using varied and complex passwords and not repeating the use of the same one.