How to add chemistry draw

how to add chemistry draw so to be able to raw carbohydrate structure and other similar chemistry diagrams

LibreOffice is a productivity suite for general office application. It does not contain tools for every possible use case. You should install your specialised software of choice for drawing specialised diagrams.

For chemistry, AlfaSoft’s ChemDraw and ACDlabs’ ChemSketch have both been observed to integrate into documents using OpenOffice, so I suspect that they will also allow integration into LibreOffice. I do not have the tools installed myself, so I cannot say for sure.