I haver an agenda template and I need to put details from minutes of a previous meeting onto the agenda, e.g. matters arising from the minutes.
Hello! Some more info would be good to make it easier to give you a good answer. Which software are you talking about? Calc? Or in general? If this is a general question it depends on your operating system and might be off topic here.
Open the 2 documents and resize their respective window so they fit into your screen size.
Further to the answerful comment by @anon73440385, I do this all the time just as he describes. But my screen isn’t big enough to accommodate both documents fully at the same time so I arrange them to partially overlap. Then if the one I need to work on isn’t already on top, a single-click on a blank corner of the document that is needed brings it to the top. Presto! Back and forth, between one document and the other.
The technique explained by Opaque and v3oat is what I do all the time. You can use calc for one document and writer for the other, or have both of them in the same app.
@anon73440385 - You should consider moving your Comment to an Answer as I expect it will completely solve the OP’s problem (at least as it was stated).