Learn Hardcore German: Ich lese einen Ratgeber im Garten. - I am reading a guidebook in the garden.

Ratgeber is a masculine noun (its nominative form is der Ratgeber). In this sentence it’s the direct object of lesen, so it must be in the accusative case. The indefinite article ein changes to einen for masculine nouns in the accusative singular.

Why is the phrase im Garten used, and what does im stand for?

im is a contraction of in
- dem, so im Garten literally means in the garden.
Because you’re describing a location (where you are reading), in takes the dative case. dem Garten becomes im Garten.

Why don’t we say ins Garten or in den Garten here?

ins = in
- das (accusative neuter) would imply movement into the garden (“I go/read into the garden”).
in den Garten (accusative masculine) likewise implies motion toward the garden.
Since lesen in this context is a stationary action (“reading in the garden”), we use the dative form im Garten to express location, not direction.

Why does German use the simple present Ich lese where English would say “I am reading”?

German does not have a separate continuous (–ing) tense. The Präsens (simple present) covers both habitual actions and ongoing events. If you really want to stress that it’s happening at this very moment, you can insert gerade (just) or im Moment (at the moment):
• Ich lese gerade einen Ratgeber im Garten.

Why is Ratgeber capitalized?

In German, all nouns are capitalized—whether they are common nouns (like Hund, Tisch) or abstract nouns (like Freiheit, Ratgeber). This rule helps you spot nouns easily.

What is the plural of Ratgeber, and how can you tell singular from plural?

The plural of Ratgeber is Ratgeber (no change in the noun). You distinguish singular and plural by the article or by numbers:
• Singular: ein Ratgeber, der Ratgeber
• Plural: zwei Ratgeber, die Ratgeber

Can you omit the article and say Ich lese Ratgeber im Garten?

If you mean “I read advice books (in general) in the garden” as a habit, you can use the plural without an article: Ich lese Ratgeber im Garten.
But for one unspecified book you need einen Ratgeber (singular + indefinite article). Omitting the article in singular would sound ungrammatical.

Does Ratgeber only mean an advice book, or can it also mean a person or guide?

Ratgeber can mean either a guide/advisor (person) or a guidebook/self-help book, depending on context.
In your sentence, because it’s the object of lesen (“to read a Ratgeber”), it clearly refers to a book. If you wanted to say you read someone’s advice in person, you’d choose a different verb (e.g. Ich höre einem Ratgeber zu → “I listen to an advisor”).