Take the spool of thread and cut the required length.
Gently thread through the eye of a needle and thread. If nothing happens, try to wet the tip of the thread and twist it in your finger. Then try again.
You can insert the threads using a special device. It is oblong oval and the wire in the form of >. Most often sold in sets together with thread.
The wire is inserted and the thread is inserted into the ear. Then you need to take the string in hand and pull the device. The wire is soft, so is inserted and pulled out easily. The string needs to remain in the eye of a needle.
For sewing heavy fabrics, use a needle with a large eye, it is easier inserted a thick thread. But light fabric, you can sew just fine with a needle, but the thread will also need thin, which should be easily inserted into the ear.