"My suitcase is under the chair."
Translation:Valiza mea este sub scaun.
- servietă = briefcase
- valiză = suitcase
"servietă" and "valiză" are not synonyms - just like in English. The briefcase is smaller and is usually used to carry books, documents, a notebook, etc. to the office and back. The suitcase is used to pack the clothes and all other things needed on a holiday.
A simple search on Google Images will make things clear.