一、释义不同。
offer：
1、offer有“（主动）拿给，给予”的意思，相当于give，后可接名词或代词作宾语，也可接双宾语，即offer sb sth =offer sth to sb [1] 。如：
The young man offered the old man his own seat on the bus.
那个年轻人在公共汽车上将自己的座位让给了那个老人。
2、offer作“提出、表示”解。 如：
Johnson offered a new suggestion.
约翰逊提出了一个新建议。
We all went to offer congratulations.
我们都前去表示祝贺。
3、offer后接不定式，表示“主动提出做某事”。如：
He offered to drive us to the airport, but we preferred to walk there.
他主动提出送我们去机场，但我们宁愿走路去。
4. offer还有“出售”、“出价”的意思。
The next morning we offered our boat for only 6 dollars.
第二天上午我们仅以6美元出售我们的船。
They offered him 3,000 yuan to buy the laptop.
他们愿出3,000元来买他的笔记本电脑。
provide：
1、提供，供给，供应
I'll be glad to provide a copy of this.
我很愿意提供它的一个副本。
2、规定; 提供(+for); 装备; 预备
The treaty provides that,by the end of the century,the United States must have removed its bases.
条约规定，到本世纪末，美国必须撤除其基地。
afford：
1、买得起;担负得起;提供;给予，如：
Today, the typical indian middle-class household can only afford a motorcycle.
如今，印度一般的中产阶级家庭只能买得起摩托车。
These industries are luxuries that only wealth and high production efficiency can afford.
这些行业都是奢侈品，只有富裕和高效生产方能提供。
二、用法搭配不同。
offer：offer sb. sth.
provide：provide sb. with sth.
afford：afford to do sth.
三、词性不同。
offer：不仅是动词还可以是名词。动词表示提供，名词表示录用信
provide：只有动词。
afford：只有动词。
参考资料：百度百科-offer
参考资料：百度百科-provide
参考资料：百度百科-afford
供给,供应,提供[(+to/for/with)]
Our farm supplies the market with fruits and vegetables.
我们的农场为市场提供水果和蔬菜。
We supply power to the three nearby towns.
我们对附近的三个城镇提供电力。
offer:
1. 给予,提供;拿出,出示[O1][(+to)]
He offered me a glass of wine.
他端给我一杯酒。
2. 愿意;试图(做某事);提议[Y][+to-v]
They offered to help me.
他们表示愿意帮助我。
He offered to lend me some books.
他表示要借给我几本书。
3. 出(价);开(价)[O1]
We offered him the calculator for US$50.
这计算器我们向他开价五十美元。
afford:
(常与can,could,be able to连用)买得起;有足够的...(去做...)
[+to-v]
They did not consider whether they could afford the time or not.
他们没有考虑是否抽得出时间。
We can't afford to pay such a price.
我们付不起这个价钱。
provide:
1. 提供[(+for)]
On Sundays his landlady provided dinner as well as breakfast.
星期天,他的女房东不但供给早餐,还供给晚餐。
2. 装备,供给[(+with)]
Somehow she managed to provide her children with food and clothing.
她总算设法使她的孩子有饭吃,有衣穿。
3. 规定[Y][+(that)]
The law provides that these ancient buildings must be preserved.
法律规定,这些古老的建筑应该保存。
4. 准备,预备