In short: With a floating rate the price of a currency is set on the market every day; with a fixed rate the state promises a set price against another currency and defends it.
Simply put: Since 1971–1973 the major currencies have floated. Between the two extremes there are bands and crawling pegs; every year the IMF describes each country's regime. The so-called "impossible trinity" applies: a country cannot at the same time have a fixed exchange rate, free movement of capital and its own monetary policy — it chooses two of the three.
Example: At a fixed rate of €1 = 1.95583 leva, a salary of 1,955.83 leva is always €1,000. With a floating rate, a fictional $1,000 may be €900 this week and €920 a month later.
Watch out: Myth: "A fixed rate is always safer." It is safe while there are reserves and trust; when they are lost, it falls suddenly — as in Argentina in 2002.
Source: IMF, Annual Report on Exchange Arrangements and Exchange Restrictions (AREAER) — https://www.imf.org/en/Publications/Annual-Arrangements-Exchange-Rates