Connect your device to the computer using its original USB cable. Tap the notification that appears on the drop-down menu and says something like "Connected as a..." or "USB Charge Only". You will see the USB computer connection options. Choose MTP or PTP from the list.
You can also open the Settings and type "USB configuration" or "USB preference" into the search bar to see the USB connection options.

Go to the official website of your phone brand to download the correct driver and install it on your computer. Here we take Samsung as an example.
Step 1. Go to https://www.samsung.com/us/support/.
Step 2. Select your product type and device name.
Step 3. Click PRODUCT INFO.

Step 4. Enter the product details and click CONFIRM.

Step 5. You will see the Software option. Click Download to download the driver for your device.

Note: If you cannot find your driver, contact Samsung customer service. If you cannot find the driver for your device on the official website of your phone's brand, contact the support team.

It is the password you've set in iTunes when backing up your iPhone to the computer. Open iTunes on your computer and you will see if the Encrypt local backup checkbox is checked. You can either remove the password by unchecking the checkbox or change the password.

Note that the old password is required on both occasions. If you forgot the password, you can use a tool to remove it.

For Reminders and Calendar, go straight to the Calendar on your Samsung device and check both of them in it.
For Ringtones and Ebooks, go to My Files, Internal storage, then enter the iMyFone folder, and you'll see the iBook folder which contains all your iPhone eBooks and the Ringtone folder which contains all your iPhone Ringtones. You should use a eBook reader to open the eBooks and a media player to open the ringtones.