First contact is when the disk of the Moon
first starts to cover the Sun
During the partial phases
you must use solar filters or projection techniques
to safely observe the Sun.
It takes about an hour
for the moon to completely cover the Sun.
The last bit of the Sun is the "diamond ring".
"Second Contact" - totality!
"Third contact"! Put back on your filters!
The last hour the moon gracefully exits, uncovering the Sun.
As the last bit of the moon leaves the Sun,
it is "Fourth contact"
and the end of the eclipse.