die Kraft
strength
The physical strength or energy of a person or animal.
Er hat nicht genug Kraft, um die schwere Kiste allein zu heben.
He doesn't have enough strength to lift the heavy box by himself.

strength / force
Loading your saved state.
strength
The physical strength or energy of a person or animal.
Er hat nicht genug Kraft, um die schwere Kiste allein zu heben.
He doesn't have enough strength to lift the heavy box by himself.

The noun 'die Kraft' (strength/force) belongs to the word family of the adjective 'kräftig' (strong). A person who has a lot of strength is 'kräftig' (strong).
Für diese Arbeit braucht man einen kräftigen Helfer.
For this work, you need a strong helper.
The phrase 'aus eigener Kraft' means that someone accomplishes something without outside help. It is often used to emphasize independence and achievement.
Sie hat das Unternehmen aus eigener Kraft aufgebaut.
She built the company through her own efforts.
When referring to physical or mental strength, 'Kraft' (strength) is often used with verbs such as 'haben' (to have), 'brauchen' (to need), 'sammeln' (to gather), or 'kosten' (to cost/take).
Nach der langen Wanderung hatte ich keine Kraft mehr.
After the long hike, I had no strength left.
To describe an abstract or metaphorical force, the genitive or the preposition 'von' (of/from) is often used. Typical examples are 'die Kraft der Natur' (the force of nature) or 'die Kraft der Worte' (the power of words).
Die Kraft der Musik kann Menschen tief berühren.
The power of music can deeply move people.
In the meaning of 'employee' or 'worker', 'Kraft' is used almost only as the second part of compound nouns. Examples are 'Arbeitskraft' (worker/labor), 'Fachkraft' (specialist/skilled worker), or 'Lehrkraft' (teacher/teaching staff member).
Wir suchen dringend eine neue Lehrkraft für Mathematik.
We urgently need a new math teacher.
The phrase 'in Kraft treten' is used for laws and regulations and means 'to become valid'. The opposite is 'etwas außer Kraft setzen' (to invalidate/suspend something).
Die neue Regelung tritt ab nächstem Monat in Kraft.
The new regulation comes into force starting next month.
employee
'der Mitarbeiter' and 'die Kraft' can both refer to a person who works. 'Mitarbeiter' is the normal and general term for a person employed by a company, public authority, or organization. In this meaning, 'Kraft' is mostly used in fixed words such as 'Fachkraft' (skilled worker), 'Aushilfskraft' (temporary worker/helper), or 'Arbeitskraft' (worker/labor). On its own, 'die Kraft' for a person sounds rather technical or shortened. In everyday language, people usually say 'Mitarbeiter' when they mean a specific person in a workplace.

Für die Küche sucht das Restaurant noch eine erfahrene Fachkraft.
The restaurant is still looking for an experienced skilled worker for the kitchen.
Ein Mitarbeiter der Firma hat mir am Telefon freundlich geholfen.
An employee of the company helped me kindly on the phone.