Open an example of the amsmath package in Overleaf. To number the equations on the left we use the argument leqno. Also that each equation is separated from the one before by an.
Otherwise use equation with an asterisk symbol if you need equations without the line number.
Put your equations within an equation environment if you require your equations to get numbered. I have no problem on adding the caption manually after I insert the formula but if i want to automate the procedure it does not. Here we see how to create an equation using the begin equation and end equation commands. Usually I do this kind of work with latex but unfortunatly my editor only accept word document.