Welcome, Joanna!
The stems are thin but so many clem's have "almost dead" looking stems. It's really not a problem though not what we clematis lovers want to see on a new arrival.
Please don't fret over ugly leaves. It's the roots that are important. You can cut off any offending leaves and then put the clematis in a well prepared spot (head in sun, feet in shade). The soil should incorporate compost, manure, Epsom Salts (one tablespoon to a gallon of lukewarm water). Angle the plant towards the trellis (or whatever you choose to have it grow on). Insert a sturdy stake. Mulch the soil heavily.
The Epsom Salt drink will encourage new stems to grow.
