What is a innocuous and isoechoic thyroid nodule. also what is a heterogenous nodule with tiny cystic spaces, it measures 0.7cm?

Probably benign: Depends on the appearance on ultrasound and also on lab and clinical parameters. Usually don't biopsy this size lesion without some other indication that there's a problem, but it should definitely be followed-up over time with repeat exams.

Hard to say: It's hard to say without seeing the actual images. An isoechoic nodule is typically nonspecific and potentially falls in the indeterminate range (ie need follow up or biopsy). Same thing for a heterogenous "nodule" with tiny cystic spaces. A "complex cyst" with tiny cystic spaces can be a sponge like cyst that is typically benign.