In WordPress Permalinks mechanism, file name of a post is made by converting whole title into lowercase and replacing spaces among words with hyphens (-). If the title contains special characters like question marks (?) then those will be removed. So, if you write long titles then URLs of your posts will also be long.

This may not be preferable in some cases. Luckily WordPress has a way to modify this at its writing panel called Post Slug. Perhaps you might not have noticed it. If the text box is not visible, just click the plus mark at its right and the text box will appear. Just include the name you want there and it will be the new post slug which makes the URL. Remember to follow the mentioned rules of the mechanism.

For an example, the title of this post is “How to Write Descriptive Titles without Making URLs Long in WordPress” but the post slug is “long-titles-short-urls”.