Yep, he inherited the title from Synel before the play starts. When the witches call him Thane of Cawdor he says, "By Synel's death I know I am Thane of Glamis, but how of Cawdor?"
He was a successful general and Thane of Glamis.
In Shakespeare's Macbeth, Glamis is the castle where the play's protagonist, Macbeth, resides at the beginning of the story. Following a prophecy that he will become the King of Scotland, Macbeth murders King Duncan in his chambers at Glamis in order to seize the throne. This act sets off a chain of events that lead to Macbeth's downfall.
A Dagger
They were killed by Macbeth because he blamed them for Duncan's murder.
"I" said Macbeth, "with the servants' daggers. I killed Macbeth."
And then Macbeth asked Macbeth if he confronted Macbeth on killing Macbeth with Macbeth.
Macbeth stabbed him when he was asleep.
According to historical record he died from cutting wounds. The king's own men killed him for an unjust invasion of Macbeth's lands.
In shakesperes story it is said that Macbeth killed him in his sleep but in reality historians believe he was killed (by Macbeth) during or shortly after the battle.
Macbeth kills Duncan in his own castle at night time.
when Macbeth and banquo were returning from the battlefield, they met the weird sisters who prophesied that Macbeth will be the thane of glamis, thane of cawdor as well as the future king of Scotland. since after returning from back Macbeth was proclaimed thane of cawdor, he became ambitious and wanted to be the future king of Scotland. therefore when duncan came to visit Macbeth to honour him for his outstanding bravery, he instigated by lady Macbeth murdered duncan
He had his suspicions because the fact the Macbeth killed the servants he blamed the murder on.