How do I know that I know a word? When

How do I know that I know a word? When can I place it in category number 4? When I know how to spell it? Or when I can recognize it?

When you can recognize it.
By spelling the native speaskers also make mistakes.
But did you understand the difference between “учить” and “учиться”? - A lot of foreigners make a mistake by using these words.

when you realize you can use it in a conversation

I understand that “учить” is used with concrete topics and “учиться” requires one to explain where one studies. Right?

I find that Russian words have so many forms that it is difficult to tell when you know a word and not. Still, I’m not giving up…

The first form you can use to ‘teach someone’, your kids etc. You can use the first form when you are learning something by heart (a poem). The second form has two last letters ‘sja’ which reflects the action back onto the speaker. That means that you learn (teach yourself) to do something or you are studying. Hope it is a little bit clearer now

It’s an interesting question. I usually mark a word when I can understand it out of context - ie, I just see the word alone and know it. There are tons and tons of words I understand when reading but couldn’t easily define out of context.

Also, I don’t mark words as known if I lingq them in a text and a few times after reading the text I then think I know the word. It is too easy to forget the word later on and I have to remark it as unknown - which I hate to do. So, if I mark a word I will only mark it when I encounter it in new material.

Also, with Russian there are nuances that sometimes I just don’t get so I get annoyed and mark them and move on. For example,

стройка
застройка

I didn’t really understand even my wife’s description of the difference so I got annoyed and took them both to mean construction and moved on. I have enough problems with Russian to try and decipher such things.

Every language has some own difficulties and some easier peculiarities.
For example, the Russians can’t understand why English have so many tenses: 16 in Active and 10 in Passive. Russian has only 3 in Active and 3 in Passive Voice.
The Russians can’t understand the Sequence of Tenses, the Gerund and especially Phrasal verbs. I have a book of the English Phrasal verbs which consists of 800 pages!.. IIt’s impossible to remember!..
But we have a good wayout in every language - to take the meaning of the words in the context withourt concerning about all possibilities of theit meanings.
About your words:
“стройка”- is a construction site.
“застройка” - a housinf development of a certain arera.
“строительство” - is a process od the constructuion, building up.
And some examples with “учить” and “учиться”:
Я учу новые слова.
Я уч у (=изучаю) русский язык.
Я учусь в школе, на курсах, самостоятельно.
Она учится хорошо, плохо.
Он учится на инженера.
Good luck!

I also find it helpful to move words to known when I no longer need to use the system to check meaning. I don’t think of the stats here as an accurate record of what I’ve learned, but more a reminder that I am still learning.