Arduino MKR ZERO port, battery and connector

I can't find Arduino MKR ZERO port in Arduino IDE and the port is blanket. would you mind helping me.please?

MKRZero runs at 3.3V. The maximum voltage that the I/O pins can tolerate is 3.3V. Applying voltages higher than 3.3V to any I/O pin could damage the board.
would you mind explaining it to me, please? (is that means I only use sensors/devices which have 3.3V)
If Arduino MKR ZERO runs at 3.3V and The maximum voltage on the I/O pins 3.3V, why there are VIN=5V,5V pins on the MKRZero board?

What's the recommended type of battery?

MKR ZERO has an on-board SD connector with dedicated SPI interfaces (SPI1) that allows you to play with MUSIC files with no extra hardware!
Could you explain it, please?

I want to connect Arduino MKR ZERO with solar panel and battery.
What's the best connector that connects all of them together?