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You need well-draining potting soil. Try adding about 1/3 perlite to 2/3 potting soil. Also, be sure to let the soil dry out between watering.

my suggestion would be to remove the existing weeds, then use the soil. It may have weed seeds in it but so does all other ground dirt. The key to preventing germination is to cover the planted soil with mulch.

If you don't have an immediate need for the soil, you can cover the dirt with clear plastic, laying bricks or some kind of weights around the edges to hold the plastic in place. Then leave it for several weeks. The heat generated by the sun will kill the weed seeds.

https://agrilifeextension.tamu.edu/library/gardening/soil-solarization/

I think adding the garden soil is a great idea. Be sure to mix it in well.

It looks like the feces of some small animal! You may need to contact your local agricultural agency to find out what it is, unfortunately.

This happens when soil has quite a bit of peat moss. Using coco coir and an acidifier will make a good replacement when mixing soils.

Alternatively, it is an avoidable situation, as long as the peat never has a chance to dry out, fully. Once this happens, it is hard to get it to take water, again.

Here are some articles that will help:

https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/peat-moss-information.htm

https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/planting-in-coco-peat-media.htm

https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/peat-moss-alternatives.htm

It may not be enough sun for the plants you are growing. You should select plants that need only part sun. Also, avoid splashing water on the leaves when you water, hold the hose down into the container. Allow the soil to dry out between waterings. If the plants droop, water sooner. The brown areas could signal a fungal infection or overwatering. Remove the damaged leaves and any that fall onto the soil to help prevent further spread of any fungi.