iPhone internet outdoors

i am unable to search internet when I am outside.

When you are outside your home, use Public Wi-Fi, see -> this Apple article: Use captive Wi-Fi networks on your iPhone, iPad or iPod touch -> Use captive Wi-Fi networks on your iPhone or iPad – Apple Support (UK)

Nowadays, Public Wi-Fi is offered for free, in big cities, shopping centers, in Public Transport (bus & train), airport, restaurants and others.

That depends on where you live.

If at the moment you are away from home and there is no Public Wi-Fi, you have to use Mobile Data, for sure go to -> Settings -> Mobile network -> Mobile Data -> ON.

Could be multiple reasons and it's hard to tell without details.

Do you have cellular service? Is it active and getting a good signal?

If you are using wifi based indoors and live in a crowded area you could find other routers trying to use the same channel you are using. You would have to reconfigure your router's settings. Indoors the other signal maybe weak, but outside your home wifi is weaker and others are stronger.