Meta description tag is one of the ways to improve the representation of your site in search results (i.e. its snippet). The contents of this tag is taken into account together with fragments of the page text when the snippet is generated.
Recommendations on creating metadescriptions:
Metadescriptions should not be too short (longer than just a few words).
They must desribe a particular site page, and not the site as a whole.
Metadescriptions should be written for humans, in ordinary human language, i.e. they should be detailed, written in well-formed sentences, without abusing keywords, key phrases, caps, advertising slogans etc.
Metadescriptions should be informative. Try to express the essence of your document in a few sentences.
The content of the meta tag must be relevant and reflect the current status of the page.
Metadescriptions must be in the same language as the document.
Examples of bad metadescriptions:
Metadescriptions filled by temporary technical information, e.g.: “I should add some text here”.
Out-of-date descriptions. For example, the prices of the products sold on the site have changed, the described document is located at a different address, but the descriptions remained unchanged.
Placement of important information in the end of the text. The most important information and phrases must be placed in the beginning of metadescriptions whenever possible.