The process of forming a word using the letters of another word is called an anagram.
Unless you have other letters you're not telling us about, a word using "these" letters is "sheet."
The word is sterns
The word "river" can be spelled by using five letters from the word "university."
There is no English word that uses all 7 of these letters. The longest word using these letters in unreel. The longest word using the j is jurel.
There is only one word that can be formed using all 7 letters provided. The word that is formed is "saltbox". There are many other words that can be formed using those letters that are 6 letters or less.
ανανάς (ananás) The first word is using Greek letters, the second is using English letters.
jovial
There's no word using all the letters, here are the two longest words:tenchtenth
There are no English words you can make using only those letters.
Using all 7 letters you get rewords
Using only the first letters of a word to form a new word or phrase is called an acronym.