Laptops, tablets and mobile phones normally have an in-built microphone for recording. It is literally just a question of capturing the sound in the environment – it could be children singing or talking, playing instruments etc. As you get more confident you may want to think about plugging a microphone in. Children are capable of taking responsibility for capturing the recordings. It is always really interesting for children to hear their own work – even something as simple as their own voice when speaking or singing. When listening back, children are likely to make spontaneous comments – audio (and video) recordings are also great ways to capture work in progress, providing a useful way for children to critically engage with their own sound, commenting on it, working out what might need improving and the next steps to this, as well as providing a sound-based record of work from one week to the next. It is lovely for pupils to revisit earlier recordings at a later date too to hear musical progress and also remember the work.
If using a laptop, you could use the built-in recorder or download a programme such as Audacity – this is free and available in many languages. Audacity also has very sophisticated (yet straightforward to use) functionality to manipulate sounds. Extensive online tutorials (aimed at adults rather than children) are available - you will benefit from being familiar with this (and any other) technology before using it with pupils.