The Spanish Armada was a massive naval force launched to invade England in 1588. King Philip II of Spain attacked England for several reasons:

Religion: Spain was Catholic and King Philip wanted England to become Catholic again.
Military: Elizabeth had sent troops to help Dutch rebels fighting Spain in the Netherlands.
Marriage: Elizabeth had refused Philip's offers to marry her.
Mary: The execution of Mary Queen of Scots angered France (she had been Queen of France too). This made Philip confident that France would not side with England.
Pirates: Elizabeth encouraged Drake and others to attack Spanish ships and ports.

The Spanish Plan

Spain sent an Armada of 130 ships. They carried 34,000 soldiers and planned to pick up another 30,000 in the Netherlands. It was also expected that 25,000 English Catholics were ready to rise up in support of the invasion. They took 180 priests with them who would help to convert the English.

The Spanish fleet was led by the Duke of Medina-Sidonia who had no naval experience.

For more detail on the Spanish Armada see here (2020 Historic Environment Depth Study).

GCSE Elizabethan England 1568-1603 AQA

Causes of the Spanish Armada