Вчера я записался на бесплатный вебинар по русскому языку.

Yesterday I signed up for a free webinar on the Russian language.

Breakdown of Вчера я записался на бесплатный вебинар по русскому языку.

• я: I
• вчера: yesterday
• по: on
• русский: Russian
• язык: the language
• бесплатный: free
• вебинар: the webinar
• записаться на: to book (an appointment)

Questions & Answers about Вчера я записался на бесплатный вебинар по русскому языку.

Why is it записался and not записал?

Записаться is a common verb meaning to sign up / to register (oneself), so it’s reflexive (-ся).
Записал (from записать) usually means to write down / to record something (an object), e.g. Я записал номер = I wrote down the number.
For “sign up (for an event)”, Russian normally uses записаться.

What does the -ся part mean here?

In this sentence, -ся marks a reflexive/intransitive action: you’re not “registering someone/something,” you’re registering yourself.
So я записался = I signed up (myself).

Why is the past tense записался masculine—what if the speaker is female?

Russian past tense agrees with the subject in gender and number.

• Male speaker: я записался
• Female speaker: я записалась
• Plural (we/they): мы/они записались
  (Neuter exists too, but not with я.)

Is записался perfective or imperfective, and why does that matter?

Записаться is perfective: it presents the action as completed—I signed up (successfully).
The imperfective counterpart is записываться (or sometimes записываться на...) and would focus on the process/habit:

• Я записывался на вебинар = I was signing up / I used to sign up (context-dependent).

Why do we use на with вебинар?

With events/activities, Russian often uses записаться на + Accusative:

• записаться на вебинар = sign up for a webinar
  Other examples: на курс, на приём (к врачу), на тренировку.

What case is вебинар, and how do we know?

After на in the meaning “onto / for (an event)”, Russian typically uses the Accusative.
Here вебинар is masculine inanimate, and its Accusative form is the same as Nominative: вебинар (no visible change).

Why is it бесплатный вебинар—what is the grammar of бесплатный?

Бесплатный is an adjective meaning free (of charge) and it agrees with вебинар in:

• gender: masculine
• number: singular
• case: Accusative (which looks like Nominative for masculine inanimate)
  So: бесплатный вебинар.

What does по русскому языку mean literally, and why is it not русского языка?

по + Dative often means on the topic of / regarding / in (a subject area).
So вебинар по русскому языку = a webinar on the Russian language / about Russian.
That’s why it’s русскому языку (Dative), not русского языка (Genitive).

What case are русскому and языку, and how are they formed?

They’re both Dative singular because of по:

• русский → русскому (masculine/neuter Dative singular adjective ending -ому)
• язык → языку (common masculine Dative singular ending -у)
  So: по русскому языку.

Could I also say вебинар по русскому without языку?

Yes, in casual speech you might hear вебинар по русскому, where русскому functions like “Russian (language)” as a subject name.
But the fuller, more explicit and neutral version is по русскому языку.

Why is вчера at the beginning—can the word order change?

Russian word order is flexible. Вчера at the start sets the time frame immediately, which is very natural.
Other possible orders (with slightly different emphasis) include:

• Я вчера записался на бесплатный вебинар по русскому языку. (focus more on я)
• Я записался вчера на бесплатный вебинар... (emphasizes it was yesterday, not another day)

Do I need a pronoun like себя to show “myself” (I signed myself up)?

No. The reflexive verb записаться already contains that meaning, so я записался is complete.
You’d typically only add extra words if you contrast or emphasize, but it’s not standard here.