Every car is geared differently, that said it sounds like in both cases, you are in "too high of a gear".
Typically when making a turn from a near stop (unless on a freeway, parkway or at a high speed), you would do so in second gear. Typically, if you're not stopped, you shouldn't need to go all the way to first gear, but again, it depends on the car (with more experience, you'll get better at staying higher without bucking...).
If you're slowing down approaching a light, you need to downshift as necessary; again it depends on the car. Typically, much below 25mph, you might need to go down to 2nd gear to avoid "bucking". While you're learning, if you want, you can just step on the clutch or throw it in neutral if she's bucking and just brake (not wonderful for your brakes...).
Going uphill from a stop is one of the most challenging. You have to strike a balance between "riding the clutch" (too much wear on the clutch) and letting it out too fast (which causes "buck" or stalling). Yes, from a low speed or certainly from a stop, you might use 1st gear. You'll have to experiment. Try not to burnout the clutch...