fertigstellen
to complete
To fully finish or bring to completion a task, project, or product.
Der Handwerker wird das Bad bis Ende der Woche fertigstellen.
The craftsman will complete the bathroom by the end of the week.

to complete
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to complete
To fully finish or bring to completion a task, project, or product.
Der Handwerker wird das Bad bis Ende der Woche fertigstellen.
The craftsman will complete the bathroom by the end of the week.

`fertigstellen` (to complete) is a separable verb. The prefix `fertig-` comes at the end in a main clause. In subordinate clauses and in the infinitive with 'zu', the verb stays together.
Wann stellt ihr das Projekt endlich fertig?
When are you finally going to complete the project?
The verb `fertigstellen` (to complete) always requires an accusative object. You always complete 'something'.
Die Autorin muss ihr Manuskript bis morgen fertigstellen.
The author has to complete her manuscript by tomorrow.
`fertigstellen` (to complete) is often used with things that require a process or a longer period of work. Typical objects are: a project, a building, a report, or an order.
Die Baufirma konnte das Haus pünktlich zum Jahresende fertigstellen.
The construction company was able to complete the house on time by the end of the year.
to lock / to complete
'abschließen' and 'fertigstellen' can both mean that a task or project is completed. 'abschließen' is a little broader and can also fit an educational program, a course, or a phase. It often emphasizes: now the matter is officially or successfully finished. 'fertigstellen' fits especially well with something that is being produced or worked on, for example a house, a report, or a file. It emphasizes: the result is now finished and can be used or handed in.

Der Mitarbeiter stellt den Antrag noch vor der Reise fertig.
The employee finishes the application before the trip.
Am Freitag schließt Anna ihren Sprachkurs ab.
On Friday, Anna completes her language course.