Every author is keen to be published, but each wants to be treated fairly.
You might want to try to get advice from other published authors you know. They may be able to guide you about typical royalty rates. Be aware that these do vary not only from publisher to publisher, but also from author to author. Some publishers take different approaches to different kinds of publications including hardback books, paperback books, e-books, audiobooks, and foreign rights so check that the contract being offered to you is within an acceptable industry range.
Traditionally, publishers offered an advance on royalties. This is a payment made to the author in advance of publication, but which is reclaimed by the publisher from the royalty earnings. Today, many newer publishers offer a royalties-only arrangement and therefore often pay a higher royalty rate. This is not really a problem. Although, if an advance is paid, it may be helpful to the author and perhaps encourages the publisher to assist in promotion of the book. However, the advances paid now are usually quite small now and therefore do not make a huge difference. Even large advances referred to on the rumour mill are not what they seem to be. They may apply to contracts for more than one book and are often paid in instalments. Typically, payments are made on signing the contract, on delivering the manuscript and again on publication. Actual payments received, therefore, may be quite small and also paid over a long period of time. Traditional publishers usually pay royalties only twice a year whereas newer publishers who do not pay advances often make quarterly payments.
If you are not used to reading contracts, it is sensible to have someone to check the contract for you. That is a perfectly reasonable thing to do as you want to know that there are not any damaging clauses or unexpected restrictions imposed on you.
If you have an agent, they will negotiate the contract for you and check it over. If you do not have an agent, you should consider joining the Society of Authors https://www.societyofauthors.org/ in Britain or The Authors' Guild https://www.authorsguild.org/ in America. It is possible to join both of these organisations as an emerging author if a publishing contract has been offered to you even if you have not signed it. These organisations will be able to provide advice on the contract and its terms.
Under no circumstances should you pay a publisher to produce your novel. No reputable agent or publisher will ever ask for any upfront payment from an author.
Normal practice would be for you to pay your agent a commission from your royalties. Equally, publishers invest a great deal in the preparation, production and distribution of your book. It is usual for them to take a share of the royalty payments to cover their expenses. If you receive a request for payment by an agent to review your work or to represent you, walk away. If a publisher demands payment from you to cover the design or production of your novel, again, walk away.
Decide, bearing in mind the advice you get, if the offer you have received is good. If the royalty rates and other details are acceptable, also consider the track record of the agent or publisher and find out what their reputation is like in the industry and with the authors in their stable. Do not be shy about asking questions about anything relating to the contract if you do not understand something. They will not be aggrieved but will be happy to explain their terms and will want you to be satisfied with them.
There are many issues you may want to clarify before you sign the contract. Be sure you know which other authors are on the list of your agent or publisher and how they intend to sell your novel. Also, ask how the agent intends to work with you.
If you have been accepted by a publisher remember to ask how much time they intend to spend marketing and distributing your book and how much time they expect you to invest in that part of the business. Remember, if you are required to spend too much time publicising your first book, you may not have time to write the second.
Whatever you do, do not have unrealistic expectations. No agent or publisher can promise that your book will be successful. Issues may arise along the way from acceptance to publication and even after that. So, you must be able to approach the business with your agent or publisher with reciprocal understanding and effort. That way your association will be most fruitful.
If you decide to accept the offer, tell any agents or publishers to whom you have sent your submission. It is a courtesy, and it is worth thinking about the fact that the publishing sector is quite small and if you create goodwill early, it cannot do you any harm as your career progresses. Once you have done that and signed the contract, you can, at last, open a bottle of wine or have a frothy coffee.