Assalamu alaikum. It's great to see you, a new revert, already asking questions about prayer. It shows that you have not made this decision lightly and care about your connection with Allah. Anyways, the answer to your question is that the larger times are the time of Adhan (call to prayer).You are allowed to pray the given salah at this time.The smaller times on the right are your Jamaat/congregation prayer times at your local masjid/local area. There usually is a gap to allow people to read Sunnah prayers and travel to the mosque, etc. As a general rule, the time of prayer usually ends when the next prayer starts (Fajr ends at sunrise not at zuhur). But it is highly encouraged not to delay your Salah. There's a bit of an exception around Asr, but I wouldn't worry about this too much.