Those three words give you power to move mountains, figuratively speaking. With an offer in hand, you wield the power to hurry other companies along their process to interview you and perhaps provide an offer as well, and also gives you the power of negotiation to ensure the job you accept is exactly what you want.
Some companies will call you ahead of time and give you a “verbal offer” and highlight some of the details of your employment with them. You may be pressured to give a verbal confirmation of joining the company during that call, but a verbal agreement is not the same as signing a contract – while you can still decline a company even if you’ve given a verbal agreement to take the job, it’s important that you say something to the effect of “I’ll accept the offer to work for you contingent on reviewing the final offer, but so far it sounds great, thank you!”
An offer letter is effectively an agreement, though not usually contractually binding so even if you sign it and return it to the company, you could still back out of employment before your start date, though this should be a VERY rare move and can be risky for your reputation.
Offer letters usually require a response within a specific amount of time. If I’ve just spent a month or two finding you as the best candidate for the job and you’ve told me you can start in two weeks, then I expect you’ll tell me very soon after giving you my offer whether or not you accept employment. However, the ultimate decision is yours, and you should not feel pressured to answer immediately. In my experience, companies that put a lot of pressure on you to accept the offer are usually very aggressive in nature.
Within reason, everything outlined in your offer letter is negotiable: salary, equity, benefits, perks and allowances, start date, even the deadline to respond. There are tons of people who can mentor you on negotiation tactics once you get a written offer from the company and guide you through this.
It’s important that people of all genders/backgrounds negotiate and advocate for their own interests. White males tend to be the most aggressive with negotiations, especially regarding starting salary, and other genders and minorities fall behind quite a bit on their offers. Know what your skills are worth and fight for what’s yours.
Negotiating an offer is a big game of give and take. If I offer you a salary and equity and a nice amount of vacation time, if you come back to me and ask for more of something without giving something in return, I’m less likely to agree to changes in the offer. Perhaps you’d like more salary and give up some equity in return, or give up a parking allowance if you bike or bus to the office in return for a few extra vacation days.
While it’s true that everything in the offer is negotiable, there are limits. It’s extremely rare that the company with rescind an offer, but it can happen if the changes you request are way beyond normal. For example, if I offer you market rate as salary with 2 weeks of vacation time and you ask for 4 weeks of vacation, I’m either going to renegotiate your starting salary or tell you you can’t have more vacation time.
This is a whole other topic I can discuss with you, but it factors a lot into your total compensation. My typical advice is that equity is only worth negotiating if you plan to stay at the job for several years.