Before any software, the obligation.

VAT in the UAE is charged at 5%. You must register once your taxable supplies and imports pass the mandatory registration threshold of AED 375,000 over the preceding twelve months, or where you expect to pass it in the next thirty days. You may register voluntarily from AED 187,500. Once required, you have 30 days to apply. Source: Federal Decree-Law 8/2017 Art. 3; VAT Executive Regulation (Cabinet Decision 52/2017 as amended) Arts. 7–8.

The standard tax period is three calendar months, and the FTA can assign a different one. Your return and your payment must both reach the FTA no later than 28 days after the end of the period. Where that day falls on a weekend or public holiday it moves to the next business day. Source: VAT Executive Regulation Arts. 62, 64.

The return itself is the VAT 201. Three things about it surprise people:

1. It splits standard-rated supplies by Emirate. Boxes 1a to 1g cover Abu Dhabi, Dubai, Sharjah, Ajman, Umm Al Quwain, Ras Al Khaimah and Fujairah. This is not optional analysis — it is the shape of the form.
2. Zero-rated and exempt are different boxes. Both show no VAT. They are not interchangeable, and picking the wrong one misstates your return.
3. Some boxes are not yours to fill. Box 2 (tourist refunds) is pre-populated from the Planet Tax Free system and is not editable. Box 6 (imports) is pre-populated from your customs declarations.

The idea to carry forward: the VAT 201 is a classification exercise before it is an arithmetic one. Odoone does the arithmetic perfectly and instantly. What it cannot do is know that a supply you tagged as an export was really exempt. Lessons 4 and 12 are about making sure the classification is right.