diary
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diary
A book or file in which a person regularly records personal experiences, thoughts, and feelings. The activity is often called 'Tagebuch führen' (to keep a diary).
Als Teenager habe ich jeden Abend in mein Tagebuch geschrieben.
As a teenager, I wrote in my diary every evening.
The word 'Tagebuch' (diary) is a simple compound made up of 'die Tage' (the plural of 'der Tag', day) and 'das Buch' (book). So it is literally a 'book of days'.
In einem Tagebuch kann man seine Gedanken für jeden Tag festhalten.
In a diary, you can record your thoughts for each day.
The most common and natural way to say that you regularly write in a diary is the expression 'Tagebuch führen' (to keep a diary). The verb 'führen' (to lead/keep) is used here instead of 'schreiben' (to write) or 'machen' (to make/do).
Sie führt seit ihrer Kindheit Tagebuch.
She has kept a diary since childhood.
When talking about writing in a diary, the verbs 'schreiben' (to write) and 'eintragen' (to enter/record) are common. A single entry is called 'der Tagebucheintrag' (diary entry).
Er schrieb jeden Abend seine Erlebnisse in sein Tagebuch.
He wrote his experiences in his diary every evening.
blog
'der Blog' and 'das Tagebuch' can both contain regular texts about experiences, thoughts, or a specific topic. The difference is mainly in the place and the audience. A blog is on the internet and is usually intended for other readers. A diary is often private and written for oneself, in a notebook or in a file. Learners may confuse the words because a blog can seem like an online diary. If texts are published publicly, 'Blog' fits better; if personal notes are meant, 'Tagebuch' fits better.
Abends schreibt Tom in sein Tagebuch, was ihn am Tag beschäftigt hat.
In the evening, Tom writes in his diary about what was on his mind during the day.
Auf ihrem Blog schreibt Lena jede Woche über einfache Rezepte.
On her blog, Lena writes about simple recipes every week.