Her vague idea for a community art installation began to take shape after she sketched out her initial concepts and gathered materials.

take 在这里是动词，意思是"呈现、获得"某种状态或形式。 shape 是名词，意思是"形状、形态"，引申为"具体形式"或"明确形态"。 take shape 是一个固定短语，意思是"成形、变得具体"，指抽象的想法或计划开始变得清晰可见。