Khums is a practice by Shi'a Muslims where they give an additional 20% of their savings away, half to Shi'areligiousleaders and the other half to charity
Sadaqah is when a Muslim voluntarily gives their money and time to charity, not at a specific point during Zakah
Zakah requires Muslims to give 2.5% of their savings to charity every year
Zakah is a duty that strengthens the Muslim community (ummah) and can be donated to a Mosque or directly to charity like Muslim Aid
Giving to charity through Zakah purifies wealth, removes selfishness and greed, and strengthens the Muslim community
Zakah is only required to be paid if your wealth is greater than the nisab level
Zakah encourages Muslims to have a good attitude towards money and purifies wealth to become closer to God