can anyone explain VAT and IOSS do I need it?

Ive been doing a few international shipments lately and different for every country but I run into this VAT and or IOSS?

Can someone explain it, better than what I read online.

VAT is the UK and EU term for sales tax. If you are registered for VAT, you should enter your VAT number in the field.

EU  and UK VAT registration thresholds and rules are explained well on this website:

https://www.avalara.com/vatlive/en/eu-vat-rules/eu-vat-number-registration.html

IOSS appears to be a reform of the EU VAT system to catch smaller traders. Explained here:

https://support.sendcloud.com/hc/en-us/articles/4402393341716-How-to-add-your-IOSS-number-