When you create a table, by default it is Aligned to the left, to center it go to your properties panel and choose Center.

To resize your table you can click on the table and drag the corners, or change the Width and height in the properties panel. When you do this you will notice that by default the Cell is set to the middle and if you try to type inside the table it will type into the middle.

To change this go to your properties panel and change the Horz: Left and Vert: Top.

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