Windows 10 on Early 2015 Macbook Air (128GB)

Windows using Bootcamp uses a partition on your disk, and requires a reboot to switch and will always use all the CPU/Memory/GPU resources that are available. On a 120+ GB, disk space can be insufficient, as W10 would need about 50-60Gb for an installation.

If you are uncomfortable using VirtualBox, you can look at Parallels or VMware Fusion.

If you follow the installation guides, they are usually very simple and straightforward, unless you run into issues.

Bootcamp documentation is available at the following links.

Use Windows 10 on your Mac with Boot Camp - Apple Support

How to install Windows using Boot Camp - Apple Support

installing windows in a virtual machine like virtual box is actually less complicated then bootcamp because it being a virtual machine you need not worry about all the apple special drivers

and with bootcamp you make a fixed partition for windows where a virtual box is just a fine which inc size if you use more storage in windows

I would get them or somebody else to help you install it in virtual box rather then bootcamp, I would only really recommend bootcamp over a virtual machine if one needs to play 3d games or do 3d pro modelling or if the computer have soo little system memory that sharing it between the operating system and the virtual machine would slow everything down to a crawl

also with bootcamp you need to reboot the whole computer to switch between osx and windows

and with virtual machine you just launch the virtual machine when you need windows and close it down when you no longer need windows much shorter shift time

virtual box will not slow down your mac when it's not running

it will not make your mac more vulnerable to viruses and malware any more then bootcamp windows would in both cases malware and viruses can affect windows but not affect osx.

if you get a win10 laptop it will be as vulnerable to viruses and other infections as all other windows boxes

think you can also in case of the virtual machine place the virtual machine on an external hd so it will not cost you internal storage even if you use much storage in windows.

virus and malware are not really cross platform so windows malware is not a problem for phones or tablets or macs or linux or...