Попытка была успешной.

Because попытка is the subject of the sentence: The attempt was successful.

The nominative case is normally used for the subject in Russian, just as English uses the basic form of a noun for the subject.

• попытка = attempt
• nominative singular feminine

So in Попытка была успешной, попытка is the thing being talked about.

Была is the past-tense feminine singular form of быть (to be).

Russian usually does not use to be in the present tense:

• Попытка успешна / успешная = The attempt is successful

But in the past tense, Russian does use forms of быть:

• был = was (masculine)
• была = was (feminine)
• было = was (neuter)
• были = were (plural)

Since попытка is feminine singular, the verb must be была.

Because after была, Russian often uses the predicate noun or adjective in the instrumental case.

Here:

• dictionary form: успешный = successful
• feminine nominative: успешная
• feminine instrumental: успешной

So:

• Попытка была успешной = The attempt was successful

This is a very common pattern in Russian with быть in the past or future.

Yes. That is also possible.

There are two common ways to express this idea:

1. Попытка была успешной

   • full adjective in the instrumental
   • very standard and natural

2. Попытка была успешна

   • short-form adjective
   • also natural, often a bit more formal or bookish

Both mean essentially the same thing here.

The basic dictionary form is успешный.

It changes to match gender, number, and case.

Here are some useful forms:

• успешный — masculine nominative
• успешная — feminine nominative
• успешное — neuter nominative
• успешные — plural nominative
• успешной — feminine instrumental (and also some other forms depending on context)

In this sentence, it is feminine instrumental singular because it refers to попытка and follows была.

You can tell from both its ending and the agreement in the sentence.

1. попытка ends in -а, which is very often a feminine noun ending.
2. The verb is была, the feminine past-tense form of to be.
3. The adjective is also in a feminine form: успешной.

So all the grammar points in the same direction: попытка is feminine singular.

The standard stress is:

• попы́тка
• была́
• успе́шной

So the full sentence is pronounced:

попы́тка была́ успе́шной

Stress matters in Russian, so it is worth learning words together with their stress.

No, Russian word order is more flexible than English word order.

The neutral order is:

• Попытка была успешной.

But you may also see:

• Успешной была попытка.
• Была успешной попытка.

These alternatives can sound more literary or can shift emphasis. For ordinary use, Попытка была успешной is the safest and most neutral choice.

It most often means attempt or try as a noun.

Examples:

• первая попытка = the first attempt
• ещё одна попытка = one more try
• попытка побега = an escape attempt

So in this sentence, попытка is simply the attempt / the try.

In the present tense, Russian usually leaves out is/are.

So instead of a present form of быть, you would normally say:

• Попытка успешна.
• sometimes Попытка успешная. depending on context

The first one, with the short adjective, is especially common for a statement like The attempt is successful.

So the contrast is:

• Попытка была успешной. = The attempt was successful.
• Попытка успешна. = The attempt is successful.