A lieutenant in a standard infantry company would serve as a file closer. His basic job was to help keep the men in line and stop them from running away.
The 1st LT would in few cases give orders but the 2nd LT had no actual command job. Only if the Captain and 1st LT was lost did the 2nd LT get to give orders.
All officers where to carry a sword as their sidearm .(and symbol of authority)
And many officers also carried some sort of revolver.
Just to expand on what a LT did...
A company can be run by the captain and the sergeants and the LTs are sort of extras.
As Kautz tell us:
"23. In reality one officer is quite sufficient to attend to all the duties requiring the presence of a
commissioned officer, and if the Company would always be sure of an officer competent to do
his duty, there would probably be no Lieutenants; but it is to provide against the Company being
left without an officer that the law has provided Lieutenants.
24. The position of Lieutenant is, therefore, more one of probation and instruction, and he may
be required by the Captain to attend to all the practical duties incumbent upon the Captain himself.
The daily routine is to be present at all the principal roll-calls, drills (....)"
Their most important jobs where not in battle but during the day to day routine where they did jobs like officer of the guards and leading fatigue and working parties...
They could also be the Battalion Adjutant. Begin the one dealing with a lot of the paperwork.