I sat outside in the shadow.
My school professors were friendly.
I work like a waitress on Saturdays.
I go to my work by bicycle.
I work in a finance company.
I sat outside in the shade.
A shadow is made by your body or your hand and is too small to sit in. If it’s too hot, you sit in the shade (made by something bigger – a building or a tree, for example).
My school teachers were friendly.
Only universities have professors or lecturers. Schools have teachers.
I work as a waitress on Saturdays.
In work like, like means similar to e.g. I work like a slave. To tell someone your position at work, use as.
I go to work by bicycle.
You go to work, without my, your, his etc.
I work for a finance company.
Use in to say where exactly you work in a company, e.g. in the accounts department. To tell someone about your employer use for.