Take heed therefore unto yourselves,
and to all the flock,
over the which the Holy Ghost hath made you overseers,
to feed the church of God,
which he hath purchased with his own blood.''
The word "feed" here comes from the Greek word "poimaino", which is used 11 times in the Bible. It is translated 6 times as "feed" (John 21:16, Acts 20:28, 1Corinthians 9:7, 1Peter 5:2, Jude 1:12, Revelation 7:17), 4 times as "rule" (Matthew 2:6, Revelation 2:27, Revelation 12:5, Revelation 19:15), and 1 time as "feeding cattle" (Luke 17:7). The following definition is provided by BlueLetterBible:
The elders which are among you I exhort, who am also an elder, and a witness of the sufferings of Christ, and also a partaker of the glory that shall be revealed: Feed the flock of God which is among you, taking the oversight thereof, not by constraint, but willingly; not for filthy lucre, but of a ready mind; Neither as being lords over God's heritage, but being ensamples to the flock. And when the chief Shepherd shall appear, ye shall receive a crown of glory that fadeth not away.
1 Peter 5:1-4
Let the elders that rule well be counted worthy of double honour,
especially they who labour in the word and doctrine.
1 Timothy 5:17
"rule well" is shows up in Titus 3:8,14 as "maintain"
One that ruleth well his own house, having his children in subjection with all gravity;
(For if a man know not how to rule his own house, how shall he take care of the church of God?)
1 Timothy 3:4-5
And we beseech you, brethren, to know them which labour among you,
and are over you in the Lord, and admonish you;
1 Thessalonians 5:12
Remember them which have the rule over you...
Salute all them that have the rule over you...
Hebrews 13:7,24
Obey them that have the rule over you, and submit yourselves:
for they watch for your souls, as they that must give account,
that they may do it with joy, and not with grief:
for that is unprofitable for you.
Hebrews 13:17
To summarize, the elders/overseers/bishops are to feed the flock, or to rule over the flock. Elders have a burden for the whole flock. They talk among themselves and discuss problems as well as other things. It is good to do this behind the scenes. The following outline summarizes the specific tasks specified in the Scriptures:
1 Timothy 3:1-7-characteristics of an overseer Titus 1:6-9-characteristics of an overseer
There is no number specified. However, we know there were more than one elder at the church of Ephesus