This Ayah (2:29) is explained in detail in Surat As-Sajdah where Allah said;

﴿ظ‚ظڈظ„ظ’ ط£ظژط،ظگظ†ظ‘ظژظƒظڈظ…ظ’ ظ„ظژطھظژظƒظ’ظپظڈط±ظڈظˆظ†ظژ ط¨ظگط§ظ„ظ‘ظژط°ظگظ‰ ط®ظژظ„ظژظ‚ظژ ط§ظ„ط§ظ‘ظŒط±ظ’ط¶ظژ ظپظگظ‰ ظٹظژظˆظ’ظ…ظژظٹظ’ظ†ظگ ظˆظژطھظژط¬ظ’ط¹ظژظ„ظڈظˆظ†ظژ ظ„ظژظ‡ظڈ ط£ظژظ†ط¯ظژط§ط¯ط§ظ‹ ط°ظژظ„ظگظƒظژ ط±ظژط¨ظ‘ظڈ ط§ظ„ظ’ط¹ظژظ€ظ„ظژظ…ظگظٹظ†ظژ - ظˆظژط¬ظژط¹ظژظ„ظژ ظپظگظٹظ‡ظژط§ ط±ظژظˆظژط§ط³ظگظ‰ظژ ظ…ظگظ† ظپظژظˆظ’ظ‚ظگظ‡ظژط§ ظˆظژط¨ظژظ€ط±ظژظƒظژ ظپظگظٹظ‡ظژط§ ظˆظژظ‚ظژط¯ظ‘ظژط±ظژ ظپظگظٹظ‡ظژط¢ ط£ظژظ‚ظ’ظˆظژطھظژظ‡ظژط§ ظپظگظ‰ ط£ظژط±ظ’ط¨ظژط¹ظژط©ظگ ط£ظژظٹظ‘ظژط§ظ…ظچ ط³ظژظˆظژط¢ط،ظ‹ ظ„ظ‘ظگظ„ط³ظ‘ظژط¢ط¦ظگظ„ظگظٹظ†ظژ - ط«ظڈظ…ظ‘ظژ ط§ط³ظ’طھظژظˆظژظ‰ ط¥ظگظ„ظژظ‰ ط§ظ„ط³ظ‘ظژظ…ظژط¢ط،ظگ ظˆظژظ‡ظگظ‰ظژ ط¯ظڈط®ظژط§ظ†ظŒ ظپظژظ‚ظژط§ظ„ظژ ظ„ظژظ‡ظژط§ ظˆظژظ„ظگظ„ط§ظ‘ظŒط±ظ’ط¶ظگ ط§ط¦ظ’طھظگظٹظژط§ ط·ظژظˆظ’ط¹ط§ظ‹ ط£ظژظˆظ’ ظƒظژط±ظ’ظ‡ط§ظ‹ ظ‚ظژط§ظ„ظژطھظژط¢ ط£ظژطھظژظٹظ’ظ†ظژط§ ط·ظژط¢ط¦ظگط¹ظگظٹظ†ظژ - ظپظژظ‚ظژط¶ظژط§ظ‡ظڈظ†ظ‘ظژ ط³ظژط¨ظ’ط¹ظژ ط³ظژظ…ظژظ€ظˆظژطھظچ ظپظگظ‰ ظٹظژظˆظ’ظ…ظژظٹظ’ظ†ظگ ظˆظژط£ظژظˆظ’ط­ظژظ‰ ظپظگظ‰ ظƒظڈظ„ظ‘ظگ ط³ظژظ…ظژط¢ط،ظچ ط£ظژظ…ظ’ط±ظژظ‡ظژط§ ظˆظژط²ظژظٹظ‘ظژظ†ظ‘ظژط§ ط§ظ„ط³ظ‘ظژظ…ظژط¢ط،ظژ ط§ظ„ط¯ظ‘ظڈظ†ظ’ظٹظژط§ ط¨ظگظ…ظژطµظژظ€ط¨ظگظٹط­ظژ ظˆظژط­ظگظپظ’ط¸ط§ظ‹ ط°ظژظ„ظگظƒظژ طھظژظ‚ظ’ط¯ظگظٹط±ظڈ ط§ظ„ظ’ط¹ظژط²ظگظٹط²ظگ ط§ظ„ظ’ط¹ظژظ„ظگظٹظ…ظگ ﴾

(Say (O Muhammad ): "Do you verily disbelieve in Him Who created the earth in two Days And you set up rivals (in worship) with Him That is the Lord of all that exists. He placed therein (i.e. the earth) firm mountains from above it, and He blessed it, and measured therein its sustenance (for its dwellers) in four Days equal (i.e. all these four `days' were equal in the length of time) for all those who ask (about its creation). Then He Istawa ila the heaven when it was smoke, and said to it and to the earth: "Come both of you willingly or unwillingly.'' They both said: "We come willingly.'' Then He finished them (as) seven heavens in two Days and He made in each heaven its affair. And We adorned the nearest (lowest) heaven with lamps (stars) to be an adornment as well as to guard (from the devils by using them as missiles against the devils). Such is the decree of the Almighty, the Knower) (41:9-12).

These Ayat indicate that Allah started creation by creating earth, then He made heaven into seven heavens. This is how building usually starts, with the lower floors first and then the top floors, as the scholars of Tafsir reiterated, as we will come to know, Allah willing. Allah also said,

﴿ط£ظژط،ظژظ†طھظڈظ…ظ’ ط£ظژط´ظژط¯ظ‘ظڈ ط®ظژظ„ظ’ظ‚ط§ظ‹ ط£ظژظ…ظگ ط§ظ„ط³ظ‘ظژظ…ظژط¢ط،ظڈ ط¨ظژظ†ظژظ€ظ‡ظژط§ - ط±ظژظپظژط¹ظژ ط³ظژظ…ظ’ظƒظژظ‡ظژط§ ظپظژط³ظژظˆظ‘ظژط§ظ‡ظژط§ - ظˆظژط£ظژط؛ظ’ط·ظژط´ظژ ظ„ظژظٹظ’ظ„ظژظ‡ظژط§ ظˆظژط£ظژط®ظ’ط±ظژط¬ظژ ط¶ظڈط­ظژظ€ظ‡ظژط§ - ظˆظژط§ظ„ط§ظ‘ظŒط±ظ’ط¶ظژ ط¨ظژط¹ظ’ط¯ظژ ط°ظژظ„ظگظƒظژ ط¯ظژط­ظژظ€ظ‡ظژط§ - ط£ظژط®ظ’ط±ظژط¬ظژ ظ…ظگظ†ظ’ظ‡ظژط§ ظ…ظژط¢ط،ظژظ‡ظژط§ ظˆظژظ…ظژط±ظ’ط¹ظژظ€ظ‡ظژط§ - ظˆظژط§ظ„ظ’ط¬ظگط¨ظژط§ظ„ظژ ط£ظژط±ظ’ط³ظژظ€ظ‡ظژط§ - ظ…ظژطھظژظ€ط¹ط§ظ‹ ظ„ظ‘ظژظƒظڈظ…ظ’ ظˆظژظ„ط§ظ‘ظ‹ظ†ظ’ط¹ظژظ€ظ…ظگظƒظڈظ…ظ’ ﴾

(Are you more difficult to create or is the heaven that He constructed He raised its height, and has perfected it. Its night He covers with darkness and its forenoon He brings out (with light). And the earth, after that, He spread it out. And brought forth therefrom its water and its pasture. And the mountains He has fixed firmly. (To be) a provision and benefit for you and your cattle) (79:27-33).

It is said that "Then'' in the Ayah (2:29) relates only to the order of reciting the information being given, it does not relate to the order that the events being mentioned took place, this was reported from Ibn `Abbas by `Ali bin Abi Talhah.