das Männchen
male
A male animal, especially when it is small or considered in contrast to a female.
Das Männchen des Guppys ist viel farbenprächtiger als das Weibchen.
The male guppy is much more colorful than the female.

male / little man
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male
A male animal, especially when it is small or considered in contrast to a female.
Das Männchen des Guppys ist viel farbenprächtiger als das Weibchen.
The male guppy is much more colorful than the female.

'Männchen' (little man/male) is the diminutive form of 'der Mann' (the man). The ending '-chen' makes the word neuter, so the article is 'das'.
Alle Nomen mit der Endung -chen sind sächlich, so auch „das Männchen“.
All nouns with the ending -chen are neuter, including 'das Männchen' (the little man/the male).
This meaning is almost always used in a biological context for animals, often in direct contrast to 'das Weibchen' (the female animal).
Bei vielen Vogelarten ist das Männchen bunter als das Weibchen.
In many bird species, the male is more colorful than the female.
The action in which an animal sits on its hind legs is expressed with the fixed phrase 'Männchen machen' (to sit up). The verb in this construction is always 'machen' (to make/do).
Unser Hund kann auf Kommando Männchen machen.
Our dog can sit up on command.
In this meaning, 'Männchen' (little figure) is often combined with verbs such as 'zeichnen' (to draw), 'malen' (to paint/draw), or 'kritzeln' (to scribble). A very common form is 'das Strichmännchen' (the stick figure).
Das Kind malte ein Strichmännchen mit einem lachenden Gesicht.
The child drew a stick figure with a smiling face.
When 'Männchen' (little man) is used for a man, it can sound condescending or derogatory. It often describes a person whom one does not take seriously or finds strange.
Da stand so ein komisches Männchen vor der Tür und wollte Geld.
There was some weird little man standing in front of the door asking for money.
man
'der Mann' and 'das Männchen' are both connected to being male. 'der Mann' means an adult male person and is the normal word for humans. 'das Männchen' is mostly used for a male animal, especially in contrast to a female. It can also mean 'little man', but when used for adult humans it can quickly sound childish or condescending. Learners may confuse the words because 'Männchen' looks like a small form of 'Mann'. In everyday language, you almost always say 'Mann' for a male person, not 'Männchen'.

Bei den Vögeln hat das Männchen viel buntere Federn als das Weibchen.
Among the birds, the male has much more colorful feathers than the female.
Im Zug half ein Mann der älteren Frau mit dem Koffer.
On the train, a man helped the older woman with her suitcase.