Hi
After saving my baseline, I realized that there was an activity that was not in my schedule before. So I added that activity but now for my baseline columns, it is showing as n/a for that activity. Can I simply add dates and durations to that activitys baseline column so include it in the baseline I already saved or are there any negative consequences of doing this?

The baseline for the summary tasks will not include the newly added task. You can baseline just that task as needed.

How can I baseline just one task?

Select the task first. Then Tools > Tracking, Save Baseline for selected tasks.

i selected that task only and went where you described and it says "baseline has already been used on februyary 8 (the date i saved my baseline yesterday). are you sure you want to overwrite data in the baseline?"

so can i make this task part of baseline i saved yesterday? how?

The only way to add the task to the baseline is to re-baseline any summary task with the new task.
You may wish to save a new baseline (baseline1) to have different baselines for comparison.