As promised, today we will take a more in-depth look at the mystical imiesłowy. Joy oh joy, I know.
To do this we need to pick a nice, easy verb. How about “pisać”? And how about “napisać”? Both mean “to write”, but pisać is imperfective, and napisać is perfective.

Ready? Ok, here we go.

• piszący – active adjectival participle – (one who is) writing

This form is normally constructed using the present tense 3rd person plural form of the verb and adding “-c” plus the appropriate adjectival ending, like this:

• pisać (infinitive) – piszą (present tense 3rd person plural) – piszący, pisząca, piszące (active adjectival participle, masculine, feminine, neuter).

And it refers to an ongoing action.

See? That wasn’t too bad.
Now let’s try it with the active adverbial participle of the same verb:

• pisząc – writing (while writing, when somebody was writing something).

This is also easy to make. Just take the present tense 3rd person plural form of your imperfective verb and stick “c” to the end of it. Like this:

• pisać (infinitive) – piszą (present tense 3rd person plural) – pisząc (active adverbial participle).

It refers to an action (or state) that happens simultaneously to another action (or state).
And luckily for us, this participle doesn’t do anything extraordinary, it doesn’t decline and has no gender. Phew!

Then there’s the adverbial participle of prior action, which refers to something that has already been completed by the time the main action is taking place.
This grammatical wonder is only formed using perfective verbs and though it may look vaguely adjectivey, it doesn’t decline. And, to be perfectly honest, you won’t hear it much in casual speech. It’s the stuff that prose is made of.

But just in case, how do we make it? Like this:
Take the masculine singular past tense of the verb:

• napisał – (3rd person singular, masculine, past tense) – he wrote

Get rid of the “ł” and add “-wszy” instead:

• napisawszy – having written

To be continued…