From a Home screen, tap Phone (located in the lower-left).
You can see full specs here: Samsung Galaxy S9 Plus
Note: You can also be asked to activate the Voice assistant where you will be asked to record "Ok Google" three times.
You can also watch this video for detailed information about Google Assistant
Specs: Samsung Galaxy S9 Plus
You don't need to enable 4G as such. Just insert the 4G enabled in any slot. By default, 4G will be active. If it is not, you can change the network preferences from Network option in settings.
1. Open Settings.
2. Select "SIM & Network".
3. Select SIM Card you wish to change network preference.
4. Select the type of network and you are done.
You can check the full specs here: Samsung Galaxy S9 Plus
The Samsung Galaxy S9 is a much better phone as it gives better specifications at a similar price.
Processor: The Samsung Galaxy S9 comes with the Samsung Exynos 9 Octa 9810 processor whereas the iPhone 7 Plus comes with the Apple A10 Fusion APL1024 processor.
Camera: The Samsung Galaxy S9 has a camera of 12 MP with F2.4 - F1.5 aperture whereas the iPhone 7 Plus has a camera of 12 MP + 12 MP with F1.8 aperture.
Check Full Comparison iPhone 7 Plus and Samsung Galaxy S9