What's the best way to get mildew out of the air in a damp basement apartment?

How to get rid of mildew and excess humidity in a basement apartment by a damp forest ?
I live in this 3.5 room apartment beside a forest in Rawdon Quebec. Its being raining a lot. I can smell the mildew when I go into the city for a few days and return. My landlord gave me a dehumidifier, but I have yet to use it. I leave all the window screens open when I am here, and any mildew odor seems to go, however the forest area keeps things very humid

Im concerned about breathing in mildew, as its probably not good for the lungs or health. I also have an air purifier that puts out ozone. Would it be better to use one machine or the other, or both ? I think I also need to take a lot of my things out of boxes, and put them into sealed plastic storage containers ? I never finished unpacking all my things yet from moving in here a few months ago, so there are still several cardboard boxes

Once I get all the boxes emptied out, I can wash the wall which is closest to where the mildew is. Im in a semi basement, and on the side of this quadraplex, there is a driveway and a big field of grass beside that, Im a few feet under ground on the side, but street level in the front where there is no mildew problem. I also dont want to wreck any books. Im just not sure how to best deal with this problem, as I never had it before. I live up a mountain beside a forest, with a river running by a few hundred yards away, and a lake at the bottom of the mountain, so lots of humidity, but a cooling relief from the city,

If I start using the dehumidifier, should I leave it on when Im gone into the city for a day or two ? Ive never used one before

Thx much for your suggestions