Searching
There are two ways to search, they do different things, and they combine.
Filters narrow the catalogue by what a listing states: a city, a price ceiling, a number of bedrooms, an area drawn on a map. Exact, predictable, and free however many times you change your mind.
Words find properties that read like what you described, whether or not the listing uses your words. This is what finds the flat you could not have expressed as a filter.
Using both is usually right: the words say what you want, the filters say what you will not accept.
What happens to a sentence
Type "quiet two-bed near a park in Kreuzberg, under 600k, ready to move into" and two things happen to it.
First, it is read for the parts that are really filters. A city, a bedroom count, a price ceiling and a condition are all in that sentence, and they are pulled out and applied as filters, on top of any you set yourself.
Then what is left, the part that is not a filter, is what the search is actually run on. "Quiet" and "near a park" are not fields on any listing. They are matched against how each property reads: its description, its location, what it is. That is why a search like this finds things a filter-only search cannot, and why a listing that never uses the word "quiet" can still be the top result.
A search written in words costs one credit. Filters alone cost nothing. See credits.
Every filter
City and district are the address as the listing states it, not a radius. A property just over a boundary does not appear under the district next to it. If the thing you care about is a walk rather than a boundary, draw the area on the map instead.
A map area can be a rectangle or a shape you draw. It beats a district name whenever your real requirement is "within fifteen minutes of here".
Transaction type is sale or rent. Getting this wrong is the fastest way to a confusing result set.
Property type is apartment, house, studio and the rest.
Price, minimum and maximum, is the asking price as published.
Bedrooms and rooms are counted differently and both are available. "Rooms" follows the local convention on the listing, which in much of Europe includes the living room; "bedrooms" does not. If a result set looks like it has one room too many, this is why.
Bathrooms, minimum only.
Living area, in square metres, minimum and maximum.
Year built, minimum and maximum.
Condition is the state the agent recorded: new, renovated, needs work.
Energy label takes several at once, so you can ask for anything A to C rather than one grade.
Heating type.
Floor, minimum and maximum. A minimum excludes ground floors; a maximum is how you avoid a fifth floor with no lift, though you will want to check the lift separately.
Orientation takes several at once. Which way the windows face decides the light, and it is one of the few things about a flat that cannot be changed.
Pet friendly, parking and outdoor space are flags. Each is set when the listing states it, which is not the same as it being true: an agent who did not fill the field in is excluded by the filter regardless.
Reading an empty result
An empty result almost never means the market is empty. It means one filter was too tight, and the interface cannot tell you which.
The filter to suspect first is living area. It is the most useful field and the most often left blank, so filtering on it removes every property that did not state one, which in some markets is a third of them.
Then the flags. Pet friendly, parking and outdoor space each exclude every listing that simply did not say, and most listings do not say.
Then the boundaries. A price ceiling of 600,000 excludes a property at 605,000 that is otherwise exactly what you asked for. So does a district boundary you did not think of as a wall.
The method that works: remove filters one at a time, starting with the ones above, rather than loosening all of them at once. You are trying to find out which one was the wall, and loosening everything tells you nothing.
Reading a listing
Price history shows what was asked before. A property reduced twice is telling you something the current price is not.
Location precision says whether the pin is the building or the middle of an area. A seller may publish without the exact address, and the map says so rather than guessing. Worth checking before walking to it.
Last verified is when the record was last confirmed against its source. Anything after that date is unconfirmed rather than wrong, and on a fast-moving listing the difference matters.
Enquiring
The enquiry form routes to the agent and records that you agreed to be contacted about that property. It is the only route: agents are asked not to put phone numbers in descriptions, so that a reply is attached to the property you actually asked about.
An enquiry is also the strongest thing you can tell matching.
When you would run it again
Save it. A saved search is also an alert, so it tells you when something new matches rather than making you check.