Will this work in my laptop?

Only if your laptop takes DDR4 SO-DIMM memory. It will not fit DDR5 slots or older DDR3 machines. Check your model's memory type before buying.

Can I add it next to the memory already installed?

Yes, if the existing module is also DDR4 SO-DIMM and the laptop has a free slot. Mixing brands and speeds usually works, but the pair runs at the slower module's speed.

Does one 16GB stick run in dual channel?

No. A single module runs in single-channel mode. Two matched modules give dual-channel bandwidth, which matters more for integrated graphics than for office work.

Do I need to change BIOS settings?

Usually not. It boots at the standard 3200 MT/s profile on most machines. Some laptops cap memory speed below 3200, and then it runs at that lower speed.

Is 16GB enough for everyday use?

For browsing, office apps and streaming, yes. Heavy video editing or many browser tabs plus virtual machines may want 32GB, which means using both slots.