What does the é in Sméagol do to the pronounciation?

I've read Lord of the Rings, and I don't seem to understand what the accent is supposed to do to the pronunciation, I don't know how I'm supposed to lay pressure on the e, neither how JRR thinks there isn't enough pressure to say the name Smeagol. I know that JRR made his own language, but I can't speak it, if somebody knows why there is an accent I'd be happy to get an answer.

From Appendix E on writing and spelling:

In Sindarin long e, a, o had the same quality as the short vowels, being derived in comparatively recent times from them (older é, á, ó had been changed). In Quenya long é and ó were, when correctly2 pronounced, as by the Eldar, tenser and ‘closer’ than the short vowels.

2 A fairly widespread pronunciation of long é and ó as ei and ou, more or less as in English say no, both in Westron and in the renderings of Quenya names by Westron speakers, is shown by spellings such as ei, ou (or their equivalents in contemporary scripts). But such pronunciations were regarded as incorrect or rustic. They were naturally usual in the Shire. Those therefore who pronounce yéni únótime ‘long-years innumerable’, as is natural in English (sc. more or less as yainy oonoatimy) will err little more than Bilbo, Meriadoc, or Peregrin. Frodo is said to have shown great ‘skill with foreign sounds’.

Tolkien's phrase "as is natural in English" involves awareness of the influence of French on (British) English pronunciation. Most Englishmen, at least educated ones in Tolkien's time, would be aware that é in French is pronounced something like a shorter version of the English "ei" (as in the common loanwords café and résumé), and therefore would err on the side of pronouncing it as such in any unfamiliar word (é not being a naturally occurring letter in English, but French being the most common second language in England).

Therefore, I think the accent on the third letter in Sméagol indicates that the name should be pronounced more like SMAY-a-gol rather than SMEE-a-gol. It's not about stress, as such, although I know that accents can be used to indicate stress in some other languages (such as Russian). It's actually more like the accents used in languages like Czech and Hungarian, which are used to indicate a "longer" vowel rather than a "shorter" vowel (my "smay" versus "smee" above is an approximation of this, not exact, but an approximation which would commonly be used by "rustic" speakers such as most of the hobbits with the possible exception of Frodo).

In addition to Rand al'Thor's very nice answer I'd like to offer another route. I'm not completely sure how solid the sources I found are, so I invite everybody to find better sources to underpin (or disprove) my line of argument.

The name Sméagol is derived from an Old English word:

As for Sméagol, Tolkien explains in Guide to the Names in Lord of the Rings, “Sméagol’s name is derived from Old English sméah, an adjective meaning “creeping in, penetrating.” This word is related to the word smial, which was applied by the Anglo-Saxons to Cain, who slew his brother Abel, establishing a connotative link between Sméagol, who murdered his cousin Deagol to steal the ring.

Where Did Gollum Come From?

Similar

The name, Sméagol, comes from Old English smeagan (“to burrow”).

'Gollum' at Wiktionary

For smeagan, Wiktionary lists "smēan, smēaġean, smēġan" as alternative forms.

So we need to look at the Old English pronunciation of "éa" (or "ēa"). And according to The Encyclopedia of Arda

The name Sméagol name derives from Old English, and in that language the vowel combination éa was a diphthong, pronounced approximately like 'ai' or 'ay' in modern English. So, strictly speaking, the name should be pronounced as if it were spelt 'Smaigol' or 'Smaygol', but the alternative pronunciation as 'Smeegol' is rather more natural to speakers of modern English, and is also very common.