If you detect a lump during your self-breast examination, firstly, you should make an appointment with your doctor to get further assessment. While you are waiting for your appointment, you can check the characteristics of the lump, including its mobility, as it can help relieve some of your anxiety.
To check this, hold the lump in between your straight fingers (not the thumb) and try to move it. If the lump moves easily under the skin, it is mostly a benign lump.
You can even check if the skin the was adhered to the lump. For this, gently pinch the skin overlying the lump and move it with the fingers. If the skin did not move, it can be considered as fixed.
If the lump is fixed, there are more chances of the lump being cancerous. However, it is always recommended to consult your doctor first, before coming to any conclusions.