The particle -쯤 is a rather simple and quick to learn Korean particle. You use the particle to express your estimation of price, quantity, weight, etc. of something. As mentioned it is very simple to learn and very easy to use, so you needn’t worry.
Most of the time when we talk about quantities, prices or other things you express in number, we aren’t certain about the exact number. Oftentimes we simply give our best estimation and Koreans are no exception. To give your estimation of something, you simply need to use the particle -쯤. By attaching this particle to a noun (generally counting nouns), you indicate the number is an estimation and not a precise number. You needn’t do anything special to the sentence beyond that.
Regarding estimating prices: While you can use -쯤이다 when estimating prices, -쯤 하다 is a more common way of doing these things. However, both methods are correct!
사과가 3 000원쯤이에요. = 사과가 3 000원쯤 해요.
가: 부산행 기차표가 얼마쯤 해요?
나: 글쎄요. 56 000원쯤 할 거예요.
A: How much is the train ticket to Busan?
B: I don’t know. It’ll cost about 56 000.
How To Use
Like many other particles -쯤 is a rather simple particle to actually use in a sentence. Like those other particles, like -보다, -밖에, -만, etc., you needn’t worry about consonants or vowels at the end of the noun you want to attach it to. You simply attach it and that’s it. Because of what the particle does, this particle generally attaches itself to counting nouns.