A Hymn of Praise for Salvation  - Isaiah 12.
(Bible quotes are from the New English Bible, unless otherwise noted)
V1.
You shall say on that day:
I will praise thee, O Lord,
though thou hast been angry with me;
thy anger has turned back,
and thou hast comforted me.
NLT. In that day you will sing:
"Praise the Lord!
He was angry with me,
but now he comforts me.

The previous passage in Isaiah talks about the coming of the Messiah from the line of King David and the peace that would come when his kingdom was established in Israel.  This passage is the beginning of a response to the God who saves and restores.  God had been angry with the people of Israel, but when the Messiah comes, he will no longer be angry but will comfort his people.  This is the end of a separation between God and his people.

The coming of Christ in our lives results in the same end of separation between us and God.

V 2.
God is indeed my deliverer.
I am confident and unafraid;
for the Lord is my refuge and defence
and has shown himself my deliverer.
NLT.  See, God has come to save me.
I will trust in him and not be afraid.
The Lord God is my strength and my song;
he has become my salvation

The writer looks forward to a time when God will deliver his people from all their enemies and will keep them safe.  There will no longer be reason to fear. 

God provides for us a strong support and a reason to sing for joy.

V 3.
And you shall draw water with joy
from the springs of deliverance.
NLT. With joy you will drink deeply from the fountain of salvation!

The Spirit of God is compared with a river of fresh water in a number of places throughout the Bible.  Ezekiel 47: 1-12 gives a picture of a river flowing out of Jerusalem , bringing fresh water to refresh the land all along its banks.  Jesus promised the Samaritan woman he met at the well neasr Sychar 'living water' (John 4: 10, 13, 14).  Jesus promised the people at the Feast of Tabernacles in Jerusalem that streams of living water - the power of the Holy Spirit - would flow from those who believe in him. (John 7: 37 - 39).  When we are filled with the Holy Spirit and allow him to work in our lives, we overflow with joy.

V 4.
You shall all say on that day:
Give thanks to the Lord and invoke him by name,
make his deeds known in the world around;
declare that his name is supreme.
NLT.  On that wonderful day you will sing:
"Thank the Lord!
Praise his name!
Tell the world what he has done.
Oh, how mighty he is!

A natural response to God's love and goodness and to salvation is to praise God and to want to tell others what he has done for us.

V 6
Sing psalms to the Lord, for he has triumphed,
and this must be made known in all the world.
Cry out, shout aloud, you that dwell in Zion,
for the Holy One of Israel is among you in majesty.

Our proper response to God's goodness and his willingness to love and accept us no matter who we are and what we have done is to praise and worship him and to spread the word about his goodness and what he has done to bring salvation to all people and to restore the relationship he originally intended between us and him.