1. Explain it simply
至少 (zhìshǎo) means 'at least' or 'no fewer than'. It puts a floor under an amount or a requirement.
Word order: Subject + 至少 + number-measure / verb phrase. 至少 comes right before the quantity it limits.
Say 至少要一个小时 (needs at least one hour) or 至少锻炼三次 (works out at least three times).
Keep 至少 in front of the quantity - do not push it to the end or slide it between a number and its measure word.
2. Show examples
他至少要一个小时。
Tā zhìshǎo yào yī gè xiǎoshí.
Sandhi:Tā zhìshǎo yào yí gè xiǎoshí.
He needs at least one hour.
至少 sits before the amount 一个小时
他一个星期至少锻炼三次。
Tā yī gè xīngqī zhìshǎo duànliàn sān cì.
Sandhi:Tā yí gè xīngqī zhìshǎo duànliàn sān cì.
He works out at least three times a week.
至少 goes right before the verb 锻炼
这个箱子至少有二十公斤。
Zhège xiāngzi zhìshǎo yǒu èrshí gōngjīn.
This box weighs at least twenty kilograms.
at least this much weight
3. Share a tip
Put 至少 right before the quantity - say 至少三次, not 三次至少.