What are leveraged "ETFs" about? And what are the differences with other average or normal ETFs?

You might find one of our articles useful: Ultimate List of LEVERAGED Stock ETFs - The InvestQuest.

To answer your question,

“Normal” ETFs: These aim to replicate the underlying index as closely as possible. They achieve this either through physical replication (e.g. a stock ETF that directly holds the stocks of the index) or through financial derivatives.

Leveraged ETFs: These aim to amplify the returns of an underlying index.

They achieve this using financial derivatives (such as options or equity swaps) and debt.

It is common to find Leveraged ETFs that track 2x or 3x the DAILY performance of a stock index. For example, if S&P 500 Index is up 1% in a day, the ProShares UltraPro S&P 500 ETF that tracks 3x the daily performance of the S&P 500 Index will be up by approximately 3% on that same day.

Very importantly, note that 3x Leveraged ETFs may NOT give you 3x the Index Return over time! For example, “S&P 500 Index” was UP 4.9%** **year-to-date as of 9 August 2020, while 3x leveraged “ProShares UltraPro S&P 500 ETF” was DOWN 19.7% over the same time period.

See our article for a discussion on when is the optimal time to use leveraged stock ETFs: Ultimate List of LEVERAGED Stock ETFs - The InvestQuest