how to store array of files in appian

You will have to store those file on Appian and then write their ID to database. 

because I'm able to store the docs in local variable array I'm having difficulty with storing in the database.

because I'm able to store the docs in local variable array I'm having difficulty with storing in the database.

In a file upload field, set the value as a number field that might be in your CDT. Same should be the saveInto. 
Also, add a constant in the targetFolder of the fileUploadField in which you wat to store the document. 

Now your CDT field will automatically have the ID of the document. You can write that data in the DB and use it later. 
docs.appian.com/.../File_Upload_Component.html

Yes I have used the file upload for the multi-doc. I am able to upload multiple files in a local array and display on the screen I am having difficulty to upload it into database. I am sharing my code might help you understand what I have done and then you'll have a clear understanding of what to recommend to me. Following is the code.

/*the file upload part*/
a!fileUploadField( 
        label: "UPLOAD FILE",
        labelPosition: "ADJACENT",
        target: cons!P_XYZ_POINTS_TO_DOCS_FOLDER,
        maxSelections: 10,
        value:  
        /*local!docsList*/
        /*ri!userRequest['recordType!{20eafdce-4cae-46cf-982b-f8f20745d009}P_XYZ_REQUEST.fields.{43660766-6686-47e3-b5b2-1035686940b5}requesteddoc']*/
        local!docsList,
        saveInto: 
        /*local!docsList*/
        /*ri!userRequest['recordType!{20eafdce-4cae-46cf-982b-f8f20745d009}P_XYZ_REQUEST.fields.{43660766-6686-47e3-b5b2-1035686940b5}requesteddoc']*/
        local!docsList,
        validations: {}
      ),
/*the button that will upload in recordtype.*/
a!buttonWidget(
            label: "UPLOAD",
            value: local!docsList,
            saveInto: /*a!save(*/
              /*ri!userRequest['recordType!{20eafdce-4cae-46cf-982b-f8f20745d009}P_XYZ_REQUEST.fields.{43660766-6686-47e3-b5b2-1035686940b5}requesteddoc'],*/
              /*save!value*/
            /*)*/
            a!forEach(
              items: local!docsList,
              expression: a!save(
                ri!docs['recordType!{10edbd5a-0ae8-47a9-bda2-f80cd3efc550}P_XYZ_DOC.fields.{ad42aed6-1664-4257-97f8-1c06e7f5604b}reqDoc'],
                save!value
              )
            ),
            style: "NORMAL"
          )