how is it constructed?
First the site of construction was to be decided followed by the purchase of material as per budget. The source of man-power was from the local lordship, and the tenants would already have the necessary skills of felling trees, digging, and working timber necessary for an earth and timber castle. In terms of time, it has been estimated that an average sized motte – high and wide at the summit – would have taken 50 people about 40 working days.
Castle
Once the site of a castle had been selected – whether a strategic position or one intended to dominate the landscape as a mark of power – the building material had to be selected. An earth and timber castle was cheaper and easier to erect than one built from stone. The costs involved in construction are not well-recorded, and most surviving records relate to royal castles. A castle with earthen ramparts, a motte, timber defences and buildings could have been constructed by an unskilled workforce. The source of man-power was probably from the local lordship, and the tenants would already have the necessary skills of felling trees, digging, and working timber necessary for an earth and timber castle. Possibly coerced into working for their lord, the construction of an earth and timber castle would not have been a drain on a client's funds. In terms of time, it has been estimated that an average sized motte – high and wide at the summit – would have taken 50 people about 40 working days. 
who brought the idea of castles to england Discussions have typically attributed the rise of the castle to a reaction to attacks by Magyars, Muslims, and Vikings and a need for private defence. The breakdown of the Carolingian Empire led to the privatisation of government, and local lords assumed responsibility for the economy and justice. where did it get the name from? It is derived from the Latin word "castellum", which is a diminutive of the word "castrum", meaning "fortified place".
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Castle [SEP] Construction
Once the site of a castle had been selected – whether a strategic position or one intended to dominate the landscape as a mark of power – the building material had to be selected. An earth and timber castle was cheaper and easier to erect than one built from stone. The costs involved in construction are not well-recorded, and most surviving records relate to royal castles. A castle with earthen ramparts, a motte, timber defences and buildings could have been constructed by an unskilled workforce. The source of man-power was probably from the local lordship, and the tenants would already have the necessary skills of felling trees, digging, and working timber necessary for an earth and timber castle.